Tehran Convention 2003: Caspian Sea Framework Convention

The Tehran Convention is the framework treaty that binds the five Caspian littoral states to protect the world’s largest enclosed inland water body. Two of its four protocols are now in force (Aktau 2016 and Moscow 2023); the EIA Protocol has been ratified by all five states but is not yet formally in force, and the biodiversity protocol still awaits ratification by Azerbaijan and Russia.

Background: UNEP Regional Seas + Caspian Environment Programme 1995

The Caspian Sea is among the most distinctive water bodies on Earth. It is the largest enclosed inland body of water in the world at approximately 371,000 km² of surface area, larger than every freshwater lake on Earth, deeper than most regional seas at a maximum depth of approximately 1,025 metres in the southern basin, and brackish rather than fresh, with a salinity of approximately 12 to 14 PSU. The basin is bordered by five littoral states with deeply asymmetric political, economic, and ecological relationships with the water body, contains some of the most productive hydrocarbon fields on Earth, hosts the population of the beluga sturgeon (Huso huso) that historically supplied approximately 90 percent of the world’s wild caviar, and supports the only endemic Caspian seal (Pusa caspica).

By the late 1980s and early 1990s the Caspian had become a recognised environmental crisis. The dissolution of the USSR in 1991 transformed the riparian map from two states (the Soviet Union and Iran) to five (Azerbaijan, Iran, Kazakhstan, the Russian Federation, Turkmenistan) and triggered intense competition over the legal status of the basin and the partition of its hydrocarbon resources. The Volga River, by far the largest single tributary, was carrying enormous loads of nutrients, persistent organic pollutants, and heavy metals from a catchment of approximately 1.36 million km² covering roughly forty percent of European Russia, draining a population of more than 60 million. Offshore oil and gas exploration was expanding rapidly, especially in Azerbaijani and Kazakhstani waters. The endemic sturgeon stocks were collapsing under poaching pressure during the chaotic post-Soviet decade. In 1999 the comb jelly Mnemiopsis leidyi, already infamous from its Black Sea invasion of the 1980s, was confirmed in the Caspian and within five years had decimated the kilka anchovy fishery.

The United Nations Environment Programme had launched its Regional Seas Programme in 1974 with the Mediterranean as the pilot region under the Barcelona Convention. By the 1990s the programme had grown to encompass eighteen regional seas, of which the Caspian had been delayed by the Soviet-Iranian bilateral monopoly through the Cold War. In 1995 UNEP launched the Caspian Environment Programme (CEP) as a pre-treaty cooperation framework. The CEP operated as a GEF-funded technical and political preparation platform with offices in Tehran, Baku, Aktau, and Astrakhan, conducted the first basin-wide environmental assessment, prepared the Transboundary Diagnostic Analysis published in 2002, and laid the institutional groundwork for the Convention. The CEP was supported by the Global Environment Facility (GEF), UNEP, UNDP, the World Bank, and the European Union, with parallel contributions from the five littoral states.

2003 Tehran signing + 2006 entry into force

The Framework Convention for the Protection of the Marine Environment of the Caspian Sea was opened for signature at Tehran on 4 November 2003 and signed the same day by all five littoral states. The choice of Tehran reflected Iran’s hosting role for the parallel CEP regional centre and Iran’s long-standing diplomatic engagement with basin governance. The 2003 Convention is a framework treaty in the classic UNEP Regional Seas style: it sets out general environmental protection obligations, establishes a Conference of the Parties and a Secretariat, and provides for subsequent thematic Protocols containing operational detail.

The framework character means that the substantive obligations are couched in general language, including the duty to take “all appropriate measures” to prevent, reduce, and control pollution from land-based sources, from sea-bed activities, from vessels, from atmospheric deposition, and from dumping. The Convention’s geographic scope under Article 2 covers the Caspian Sea proper plus coastal waters, explicitly including the Volga delta, the Kara-Bogaz-Gol lagoon, and the immediate hinterland of all five littoral coasts. The Convention does not delimit maritime boundaries (those were left to bilateral negotiation and ultimately to the 2018 Legal Status Convention).

Ratification proceeded over approximately three years. Iran ratified in 2005; Kazakhstan and Turkmenistan ratified in early 2006; the Russian Federation and Azerbaijan ratified in mid-2006. The Convention entered into force on 12 August 2006 in accordance with Article 31, which required ratification by all five. The 2006 entry into force shifted the basin from soft-law CEP cooperation to a binding multilateral environmental regime, even if substantive obligations remained at the framework level pending the implementing Protocols. The Convention Secretariat, administered by UNEP, is based in Geneva (UNEP/ROE, 11 ch. des Anémones, 1219 Châtelaine).

The Conference of the Parties (COP) meets on a rotating basis among the five littoral capitals. COP-1 was held at Baku, Azerbaijan, May 2007; COP-3 at Aktau, Kazakhstan, August 2011 (where the oil-pollution protocol was adopted); COP-4 at Moscow, December 2012 (land-based sources protocol); COP-5 at Ashgabat, Turkmenistan, May 2014 (biodiversity protocol); the First Extraordinary COP at Moscow, July 2018 (EIA protocol); COP-6 at Baku, October 2022; and COP-7 in the Islamic Republic of Iran, in preparation as of 2024-2026. A Fifth Caspian Summit in Ashgabat has been discussed for 2026 in the context of Iran’s pending ratification of the Legal Status Convention.

The four implementing protocols: adoption dates, entry into force, and ratification status

The four protocols form the operational core of the Tehran Convention regime. Their adoption dates, entry-into-force dates, and ratification chronology are summarised in the table below.

As of June 2026, two of four protocols are in force: the Aktau Protocol (2016) and the Moscow Protocol (2023). The EIA Protocol was adopted on 20 July 2018, and Iran’s ratification on 30 July 2025 made all five littoral states parties (Iran was the fifth and final state to ratify), but the Secretariat has not published an entry-into-force date, so the protocol is not yet formally in force. The Ashgabat Biodiversity Protocol also requires ratification by all five Parties; Azerbaijan has not ratified and Russia has not ratified, meaning that protocol cannot yet enter into force either. A fifth protocol on Monitoring, Assessment and Information Exchange is under negotiation and has not yet been adopted.

The 5 contracting parties

The five Contracting Parties to the Tehran Convention are the five littoral states of the Caspian Sea. Each presents a distinctive implementation profile shaped by its hydrocarbon profile, institutional capacity, and relationship with wider international environmental regimes.

The Republic of Azerbaijan has the central position on the western Caspian coast and the highest density of offshore hydrocarbon activity, including the supergiant Azeri-Chirag-Gunashli (ACG) oil field complex operated by the BP-led AIOC consortium and the Shah Deniz gas-condensate field. The Azerbaijani coast is approximately 825 kilometres long and includes the major port of Baku, the largest Caspian port and the historic centre of Caspian oil production since the late nineteenth century. Azerbaijan ratified the Tehran Convention in mid-2006, has ratified the Aktau and Moscow protocols and the EIA protocol, but has not yet ratified the Ashgabat Biodiversity Protocol.

The Islamic Republic of Iran has the southern Caspian coastline, the deepest part of the basin (the southern basin reaching 1,025 metres), and the most complete biological-resource portfolio. The Iranian coast is approximately 657 kilometres long and includes the major ports of Anzali, Noshahr, Amirabad, and Bandar Torkaman. Iran ratified the Tehran Convention in 2005, ratified the Moscow Protocol (May 2014), and on 30 July 2025 became the fifth and final littoral state to ratify the EIA Protocol, making all five states parties to it (the Secretariat has not yet published an entry-into-force date for that protocol). Iran has not ratified the 2018 Convention on the Legal Status of the Caspian Sea, which has consequently not entered into force.

The Republic of Kazakhstan has the long north-eastern Caspian coastline (approximately 2,320 kilometres, the longest of any Contracting Party), the supergiant Kashagan oil field (proven reserves approximately 13 billion barrels), and the supergiant Tengiz oil field on the north-eastern coastal plain. Kazakhstan ratified the Aktau Protocol last (18 March 2016), triggering its entry into force. The major port of Aktau hosted COP-3 in 2011 and the signing of the 2018 Legal Status Convention.

The Russian Federation has the north-western and northern Caspian coastline, the mouth of the Volga River (the dominant freshwater source of the basin, contributing approximately 85 percent of total inflow), and the major port of Astrakhan. Russia was the last of the five to ratify the Moscow Protocol (15 August 2023), triggering its entry into force on 13 November 2023. Russia has ratified the Aktau Protocol, the Moscow Protocol, and the EIA Protocol, but has not yet ratified the Ashgabat Biodiversity Protocol.

Turkmenistan has the south-eastern Caspian coastline (approximately 1,768 kilometres), significant offshore hydrocarbon activity in the Block 1 and Cheleken areas, and the major port of Turkmenbashi. Turkmenistan hosted COP-5 in Ashgabat in 2014, where the Biodiversity Protocol was adopted, and is one of two states (alongside Iran) that signed the Biodiversity Protocol at COP-5. Turkmenistan has ratified all four protocols, including the Biodiversity Protocol.

Pre-2003 sovereignty dispute over Caspian legal status

The Caspian Sea was the subject of an intense and protracted sovereignty dispute through the post-Soviet period that materially constrained Tehran Convention negotiation and implementation. The legal status of the Caspian had been fixed under the bilateral Soviet-Iranian regime by the Treaty of Friendship of 1921 and the Treaty of Commerce and Navigation of 1940, which established a condominium regime with freedom of navigation and freedom of fishing within a 10-nautical-mile coastal zone for each Party. Neither instrument addressed seabed delimitation because there was no significant offshore hydrocarbon activity in the Caspian at the time.

The dissolution of the USSR in 1991 created an immediate sovereignty problem. The successor states and Iran disagreed over whether the Caspian was a sea (UNCLOS rules: territorial seas, EEZs, continental shelves), a lake (condominium rules: all five states share equal rights over the entire water body and seabed), or a body of water with neither status (requiring a sui generis negotiated regime). Azerbaijan and Kazakhstan, with the largest offshore hydrocarbon reserves, favoured a sea classification with median-line seabed division. Iran, with the smallest offshore reserves, initially favoured a lake classification with five-way equal division. Russia evolved from the lake position to a hybrid approach through the 1990s. Turkmenistan generally aligned with median-line division but had a separate dispute with Azerbaijan over the Serdar/Kapaz field.

The dispute had several practical consequences. Bilateral seabed delimitation agreements were concluded between Russia-Kazakhstan (1998), Russia-Azerbaijan (2001), and Kazakhstan-Azerbaijan (2001), establishing modified median-line boundaries in the northern basin. The southern part (between Iran, Azerbaijan, and Turkmenistan) remained without delimitation. Joint enforcement of environmental rules was constrained: the Tehran Convention’s framework character partly reflected the inability to negotiate detailed protocols without a settled legal status.

2018 Aktau Convention on legal status: “special legal status”, not yet in force

The Convention on the Legal Status of the Caspian Sea was signed at the Fifth Caspian Summit in Aktau on 12 August 2018 by the heads of state of the five littoral states. This Legal Status Convention is distinct from the 2011 Aktau Protocol on oil spill response under the Tehran Convention despite the similar venue name. It represents the largest single advance in Caspian international law since the dissolution of the USSR in 1991.

The 2018 Legal Status Convention declares in Article 1 that the Caspian Sea is a body of water with a “special legal status” that is neither a sea nor a lake under UNCLOS. The formula was a diplomatic compromise that recognised the unique character of the basin without forcing any Party to abandon their historical position. The substantive provisions establish a 15-nautical-mile territorial sea for each littoral state, a 10-nautical-mile fishery zone beyond the territorial sea, freedom of navigation for all littoral-state-flagged vessels through the entire basin, a prohibition on military presence by non-littoral states, a seabed delimitation by bilateral agreement between adjacent and opposite littoral states, an environmental protection clause explicitly referencing the Tehran Convention as the implementing instrument, and a subsea pipeline clause permitting trans-Caspian pipelines subject to environmental impact assessment.

As of June 2026 the Convention on the Legal Status of the Caspian Sea has NOT entered into force. Four of the five littoral states (Russia, Azerbaijan, Kazakhstan, Turkmenistan) have ratified it. Iran has not ratified, and without all five ratifications the convention cannot enter into force under Article 22. The principal Iranian objection concerns the definition of offshore territorial baselines under Article 1, which affects Iran’s geographic share because of the concave configuration of its Caspian coastline. Iran’s ratification of the EIA Protocol on 30 July 2025, which made it the fifth and final party to that protocol, is read by observers as a positive signal for the broader legal-status ratification.

Geographical scope: ~371,000 km² largest enclosed inland water body

The Caspian Sea covers a surface area of approximately 371,000 km² at current sea level, making it the largest enclosed inland body of water on Earth by surface area. It is larger than every freshwater lake in absolute terms, larger than the next two largest lakes (Lake Superior at 82,100 km² and Lake Victoria at 68,800 km²) combined and several times over, and represents approximately 44 percent of the total combined surface area of all enclosed lakes on Earth. The basin extends from approximately 36° N (the southern Iranian coast) to approximately 47° N (the northern Russian coast), a north-south extent of approximately 1,200 kilometres, with an east-west extent varying from approximately 200 kilometres in the central basin to approximately 450 kilometres in the southern basin.

The Convention’s geographic scope under Article 2 covers the Caspian Sea proper plus a coastal-zone extension including coastal wetlands, estuaries, lagoons, and the immediate hinterland, explicitly including the Volga delta (the largest river delta in Europe at approximately 27,000 km²) and the Kara-Bogaz-Gol lagoon (approximately 18,000 km², connected to the Caspian by a narrow strait with extreme salinity of approximately 350 PSU).

The basin divides into three sub-basins. The Northern Caspian is the shallow shelf area north of the Apsheron-Cheleken fault zone, with depths predominantly under 25 metres, covering approximately 80,000 km² of surface area but only about 1 percent of total basin volume. The Middle Caspian covers approximately 138,000 km² with depths to approximately 788 metres in the Derbent depression. The Southern Caspian is the deepest sub-basin, approximately 153,000 km² and depths to the maximum 1,025 metres, holding approximately 66 percent of the basin’s total water volume of approximately 78,200 km³. The unequal volume distribution has major consequences for pollution response: surface events in the shallow Northern Caspian have outsized ecological impacts compared to the same volume spilled into the deep Southern sub-basin.

Hydrography: max ~1,025m, avg ~211m, ~-29m below sea level and falling

The Caspian Sea’s hydrographic profile is dominated by the extreme depth contrast between the shallow Northern Caspian and the deep Southern Caspian. The maximum depth is approximately 1,025 metres in the central southern basin, the average depth is approximately 211 metres, and the depth distribution is strongly bimodal: large areas are either under 50 metres (the Northern Caspian and coastal shelves) or over 500 metres (the central abyssal plains of the Middle and Southern Caspian).

The Caspian water level is below the world ocean datum. As of 2024-2025 the sea level has reached approximately -29 metres relative to the world ocean datum, an all-time recorded low, having fallen from approximately -27 metres in the late 1990s. The basin is therefore one of the most pronounced endorheic depressions on Earth, exceeded in elevation drop only by the Dead Sea (-432 metres) and the Sea of Galilee (-211 metres). The negative elevation reflects the basin’s complete hydrologic isolation: there is no outlet to the world ocean, no surface connection to the Aral Sea or the Black Sea, and no significant subsurface drainage. Total inflow (river inflow plus precipitation plus minor groundwater) must balance total outflow (evaporation plus minor groundwater outflow).

The current sea level decline is documented at approximately 2 metres cumulative drop from 2006 to 2024 based on satellite altimetry from the TOPEX/Poseidon, Jason-series, and Sentinel-3 missions. NASA data show the decline rate was approximately 7 centimetres per year through 2020, then accelerated, with some measurements recording drops of 20 to 30 centimetres per year since 2020. The decline has substantial ecological and economic consequences: loss of shallow Northern Caspian habitat, stranding of port infrastructure (Aktau, Atyrau, and other ports require progressive dredging), conversion of formerly inundated Volga delta wetlands to dry steppe, and compression of sturgeon spawning habitat in river-mouth zones.

Brackish salinity ~12-14 PSU

The Caspian Sea is brackish, with a salinity of approximately 12 to 14 PSU intermediate between fresh water (0 to 0.5 PSU) and the open ocean (35 PSU). The salinity is approximately one-third of the open ocean and roughly half the Black Sea’s average (17 to 18 PSU). The distribution by sub-basin runs approximately 12 PSU in the Northern Caspian (where the Volga freshwater plume diffuses across the shallow shelf), 12 to 13 PSU in the Middle Caspian, 13 PSU in the Southern Caspian, and approximately 350 PSU in the Kara-Bogaz-Gol lagoon centre during normal evaporation conditions.

The brackish salinity has major biological and chemical consequences. The Caspian fauna is dominated by endemic species that evolved to this unique salinity: the sturgeon (Huso huso, Acipenser gueldenstaedtii, Acipenser stellatus, and others), the Caspian seal (Pusa caspica), several gobies, the Caspian roach (Rutilus rutilus caspicus), and many invertebrates. The endemic fauna is intolerant of either fresh-water dilution or seawater-strength salinity, making the brackish equilibrium the essential boundary condition for the ecosystem. The chemical and pollutant partitioning behaviour at 12 to 14 PSU is also distinct from the open-ocean and freshwater regimes that dominate the global oceanographic literature, which complicates monitoring programme design under the Tehran Convention.

Major rivers: Volga (~85% inflow), Ural, Kura, Sefid Rud, Atrek

The Caspian inflow is dominated overwhelmingly by the Volga River, which contributes approximately 85 percent of the total freshwater inflow to the basin. The Volga drains a catchment of approximately 1.36 million km² across forty percent of European Russia, discharges approximately 8,000 m³/s on average (with substantial inter-annual variability driven by snowmelt patterns and reservoir management), carries approximately 18 million tonnes of sediment per year (down from approximately 30 million tonnes before the Volga-Kama hydropower cascade was built), and contributes approximately 90 percent of the total basin nutrient input. The Volga delta is the largest river delta in Europe at approximately 27,000 km², designated as a UNESCO Biosphere Reserve and a Ramsar site.

The Ural River is the second-largest contributor, draining approximately 231,000 km² across Russia and Kazakhstan, discharging approximately 360 m³/s on average, and contributing approximately 4 percent of total basin freshwater inflow. The Kura River is the dominant inflow on the western Caspian coast, draining approximately 188,000 km² across Türkiye, Georgia, and Azerbaijan, discharging approximately 575 m³/s, and contributing approximately 5 percent of total inflow. The Sefid Rud (White River), the principal Iranian inflow, drains approximately 56,000 km² of northern Iran, discharges approximately 130 m³/s on average, and contributes approximately 1 percent of total inflow. The Atrek River, the principal Turkmen inflow, drains approximately 27,000 km² of Iran and Turkmenistan, discharges approximately 9 m³/s, and contributes a negligible share of total inflow but a disproportionate share of south-eastern Caspian biodiversity importance because the Atrek mouth is a critical migratory bird and fish habitat.

The cumulative annual freshwater inflow to the Caspian is approximately 300 km³ per year, balanced by evaporation of approximately 380 km³ per year. The approximately 80 km³ per year net deficit (on a long-term mean) drives the water-level oscillation dynamics and has been widening since the mid-1990s under rising evaporation rates and reduced Volga inflow.

Volga drains 40% of European Russia

The Volga River basin covers approximately 1.36 million km² of European Russia, representing approximately 40 percent of the European Russian land area and approximately 8 percent of the entire Russian Federation territory. The catchment population is approximately 60 million inhabitants across cities including Moscow (in the upper Oka tributary catchment), Nizhny Novgorod, Kazan, Samara, Saratov, Volgograd, and Astrakhan. The catchment hosts approximately 45 percent of Russian industrial production by gross value and approximately 50 percent of Russian agricultural production.

The Volga is heavily regulated through the Volga-Kama hydropower cascade comprising eight major dams on the Volga main stem (Ivankovo, Uglich, Rybinsk, Gorky, Cheboksary, Kuibyshev, Saratov, Volgograd) plus four major dams on the Kama tributary. The cascade has a total installed hydroelectric capacity of approximately 11.5 GW producing approximately 35 to 40 TWh per year. The cascade transformed the river hydrology: the seasonal flow regime has been smoothed, the sediment load has been substantially reduced, and the water residence time has been increased. The cumulative reservoir volume of approximately 168 km³ creates an aggregate residence time of approximately 6 to 8 months across the cascade.

The Volga catchment carries an enormous pollution load to the Caspian. Principal categories are nutrients (nitrogen and phosphorus from agricultural runoff and inadequate municipal wastewater treatment, with annual loads of approximately 800,000 tonnes of nitrogen and 50,000 tonnes of phosphorus), persistent organic pollutants (PCBs, DDT, lindane, polycyclic aromatic hydrocarbons from legacy and current industrial discharges), heavy metals (copper, zinc, lead, cadmium, mercury from mining and metallurgical industries especially in the upper Kama and Volga catchments), oil hydrocarbons (from upstream petroleum production, transport, and refining), radionuclides (from past Soviet nuclear activities and the 1986 Chernobyl event, which deposited caesium-137 across the upper Volga catchment), and emerging contaminants (pharmaceuticals, personal care products, microplastics). The cumulative Volga load is estimated at approximately 70 to 75 percent of the total Caspian pollution input.

Aktau Protocol on oil pollution response (2011, in force 25 July 2016)

The Protocol on Regional Preparedness, Response and Cooperation in Combating Oil Pollution Incidents was opened for signature at the COP-3 Aktau Summit on 12 August 2011 and entered into force on 25 July 2016 following ratification by all five Contracting Parties (Kazakhstan was the last to ratify, on 18 March 2016). It is the first implementing Protocol of the Tehran Convention to enter into force and the most operationally important as of 2026.

The Protocol obliges the five Parties to maintain national contingency plans, identify competent authorities and 24-hour points of contact, prepare and maintain reception facilities and pre-positioned response equipment, conduct regular joint exercises, and cooperate in mutual assistance during incidents that exceed any one Party’s response capacity. The operational coordination is delivered through a regional activity centre for combating oil pollution, hosted on a rotating basis among the five littoral capitals. The Aktau Protocol’s 2016 entry into force coincided with the start of the Kashagan field’s commercial production, which substantially raised the spill-response stakes given the supergiant scale and the shallow, ice-affected character of the Northern Caspian spill environment.

The Protocol functions as the regional equivalent of the OPRC 1990 instrument for the Caspian basin, where OPRC does not formally apply. The Aktau Protocol has been activated in practice in several minor incidents through the late 2010s and early 2020s, including small platform leaks in the ACG complex and condensate releases at Kashagan, with cooperation among the Azerbaijani, Russian, and Kazakhstani authorities under the Protocol framework.

Moscow Protocol on land-based sources (2012, in force 13 November 2023)

The Protocol for the Protection of the Caspian Sea against Pollution from Land-Based Sources and Activities was opened for signature at the COP-4 Moscow Summit on 12 December 2012 and entered into force on 13 November 2023 following ratification by all five Contracting Parties. Russia was the last to ratify, depositing on 15 August 2023. Land-based sources account for an estimated 75 to 80 percent of total pollution loads to the Caspian, with the Volga catchment alone contributing approximately 70 percent of the total pollution load, so this protocol is the most consequential of the four in terms of long-term pollution reduction potential.

The Moscow Protocol uses a discharge-control architecture similar to the 1980 Athens Land-Based Sources Protocol under the Barcelona Convention and the parallel 1992 Bucharest Land-Based Sources Protocol. Annex I lists hazardous substances whose discharge is prohibited or strictly controlled; Annex II lists substances subject to authorisation; Annex III lists factors to be considered in granting authorisations. Contracting Parties commit to applying best available techniques (BAT) and best environmental practices (BEP) to land-based discharges and to monitoring resulting concentrations in the marine environment. The Protocol explicitly addresses diffuse-source pollution from agriculture and atmospheric deposition over the basin from upstream industrial emissions.

The approximately decade-long gap between adoption (2012) and entry into force (2023) partly reflected the unresolved Caspian legal status, which complicated geographic-scope provisions, and partly reflected the institutional transition and political complications of the post-2014 period. The first basin-wide reporting cycle under the Moscow Protocol was scheduled for completion through 2025-2026. Early returns have shown substantial gaps in existing national-level monitoring networks across all five Contracting Parties, especially for diffuse-source agricultural runoff and for emerging contaminants that were not on the radar of the 2012 negotiation.

Ashgabat Biodiversity Protocol (2014, not yet in force)

The Protocol on Conservation of Biological Diversity was opened for signature at the COP-5 Ashgabat Summit on 30 May 2014 and as of June 2026 has not yet entered into force. Iran (ratified 17 October 2021), Kazakhstan (23 October 2021), and Turkmenistan (23 May 2015) have ratified. Azerbaijan has not ratified; Russia has not ratified. Entry into force requires all five Contracting Parties.

The Protocol introduces three designation categories. Caspian Protected Areas (CPAs) are designated unilaterally by each Contracting Party in waters under its sovereignty or jurisdiction. Caspian Protected Areas of Special Importance are jointly designated by all Contracting Parties, analogous to the SPAMI mechanism of the Mediterranean. Coastal landscapes of special importance for the Caspian region integrate marine and terrestrial conservation objectives, particularly relevant to the Volga delta, the Kura delta, the Iranian wetland complex, and the Turkmen coastal lagoons.

Annexes list endangered or threatened species including all Caspian sturgeon species (Huso huso, Acipenser gueldenstaedtii, Acipenser persicus, Acipenser nudiventris, Acipenser stellatus), the Caspian seal (Pusa caspica), and many endemic invertebrates, with obligations to prohibit destruction, capture, trade, and disturbance. The Protocol cross-references the Convention on International Trade in Endangered Species (CITES) and the Convention on Migratory Species (CMS). Until entry into force, species conservation in the Caspian relies on the parent Tehran Convention’s general obligations plus national law.

EIA Protocol (adopted Moscow 20 July 2018, ratified by all five states, not yet formally in force)

The Protocol on Environmental Impact Assessment in a Transboundary Context was adopted at the First Extraordinary Meeting of the Conference of the Parties (Extraordinary COP), Moscow, on 20 July 2018 (not at Ashgabat as sometimes reported; the Ashgabat venue on 12 August 2018 was the parallel summit for the Legal Status Convention). Iran deposited its ratification instrument on 30 July 2025, becoming the fifth and final littoral state to ratify and making all five Contracting Parties parties to the protocol. Azerbaijan (27 June 2019), Russia (13 December 2019), Turkmenistan (22 August 2020), and Kazakhstan (4 October 2021) had ratified earlier. As of June 2026 the Tehran Convention Secretariat has not published an entry-into-force date for the protocol, so it is not yet formally in force.

The Protocol obliges the five Contracting Parties to notify each other of planned activities likely to have significant adverse transboundary environmental impact, conduct EIA procedures with public participation extending to affected populations of neighbouring Parties, consult with affected Parties before authorising the activity, and maintain a register of EIA outcomes for Secretariat review. The Protocol applies to offshore hydrocarbon exploration and production, submarine pipelines, port and coastal infrastructure, dredging operations, dumping, river-basin water management projects affecting Caspian inflow, and large industrial installations in the coastal zone.

The EIA Protocol is the Caspian-region equivalent of the 1991 UNECE Espoo Convention on transboundary EIA. Once it formally enters into force, it will have direct practical significance for the trans-Caspian gas pipeline question: a pipeline from Turkmenistan to Azerbaijan routing Turkmen gas to European markets via the South Caucasus Pipeline and TANAP-TAP would require full transboundary EIA procedures under this Protocol, with participation from Russia and Iran whose Caspian waters would be traversed or affected.

Caspian oil + gas resources: ~50 bn bbl, ~9.2 tcm gas

The Caspian basin is the world’s largest enclosed-basin hydrocarbon province by combined oil and gas resources. Proven oil reserves are estimated at approximately 48 to 52 billion barrels (the EIA central estimate: 50 billion barrels), proven natural gas reserves at approximately 9.2 trillion cubic metres, and probable plus possible additional resources extend the resource base substantially in both categories.

The basin’s hydrocarbon resources are distributed asymmetrically. Kazakhstan holds the largest share by oil (approximately 25 to 30 billion barrels of proven oil equivalent), driven by Kashagan, Tengiz, and Karachaganak. Azerbaijan holds the second-largest share by oil (approximately 7 to 10 billion barrels), driven by the ACG complex. Turkmenistan holds the largest share by gas (approximately 5 to 7 trillion cubic metres of proven gas in the Caspian sector). Iran holds smaller offshore reserves (approximately 1 to 2 billion barrels of oil and approximately 0.5 trillion cubic metres of gas in the Iranian Caspian sector). Russia holds modest offshore reserves in its Caspian sector, much smaller than its onshore Volga-Urals and West Siberian fields.

The combined Caspian-region oil production was approximately 2.5 to 3 million barrels per day in 2024, with Kazakhstan (Kashagan plus Tengiz plus Karachaganak combined approximately 1.7 million b/d) and Azerbaijan (ACG complex approximately 0.7 million b/d) dominating. Kashagan produced approximately 17.4 million tonnes (about 350,000-380,000 b/d) in 2024, down 7.2 percent year-on-year due to operational issues, with ramp-up to 420,000-450,000 b/d projected as a new gas processing plant comes online in 2026. Tengiz reached approximately 700,000 b/d in 2024 with the Future Growth Project ramp-up.

Major fields: Kashagan, Tengiz, Azeri-Chirag-Gunashli, Shah Deniz

Kashagan (Kazakhstan, North Caspian Operating Company / NCOC consortium) is the largest oil discovery globally of the past forty years outside the Tengiz extension. The field sits in the shallow Northern Caspian (water depth approximately 4 metres at the field centre, in waters that freeze in winter), holds proven reserves of approximately 13 billion barrels of oil equivalent, contains highly sour high-sulphur crude requiring extensive surface processing, and had a difficult development history with first production delayed from 2005 to 2013. Kashagan exports primarily through the Caspian Pipeline Consortium (CPC) pipeline to Novorossiysk on the Russian Black Sea coast.

Tengiz (Kazakhstan, Tengizchevroil consortium led by Chevron) is the largest single oil field in operation in the basin. On the north-eastern coastal plain (technically onshore but within the Caspian basin scope), it holds proven reserves of approximately 9 billion barrels of oil and has been in commercial production since 1993. The Future Growth Project (FGP) added approximately 260,000 b/d of capacity through 2024-2025. Tengiz also exports primarily through the CPC pipeline.

Azeri-Chirag-Gunashli (ACG) (Azerbaijan, AIOC consortium led by BP) is the supergiant complex of three contiguous oil fields in the Azerbaijani Caspian, in water depths of approximately 100 to 250 metres. The complex holds proven reserves of approximately 5 to 6 billion barrels of oil and has been in production since 1997. ACG exports primarily through the Baku-Tbilisi-Ceyhan (BTC) pipeline to the Turkish Mediterranean coast.

Shah Deniz (Azerbaijan, AIOC-led consortium) is the supergiant gas-condensate field in the Azerbaijani Caspian, in water depths of approximately 50 to 600 metres. The field holds proven reserves of approximately 1.2 trillion cubic metres of gas plus 2 to 3 billion barrels of associated condensate. Shah Deniz Phase 2 came online in 2018; combined gas production in 2024 was approximately 30 billion cubic metres per year, exported through the South Caucasus Pipeline (SCP) and the TANAP-TAP corridor.

BTC, CPC, TANAP-TAP pipelines

The Caspian’s hydrocarbon exports flow through three major pipeline corridors. The Baku-Tbilisi-Ceyhan (BTC) crude oil pipeline is the principal export route for Azerbaijani crude, running from the Sangachal terminal near Baku through Georgia to the Turkish Mediterranean port of Ceyhan, 1,768 kilometres long, with design capacity of 1.2 million barrels per day, in commercial operation since 2006. BTC is the principal non-Russian export route for Caspian crude.

The Caspian Pipeline Consortium (CPC) pipeline is the principal export route for Kazakhstani crude, running from the Tengiz field through southern Russia to the Russian Black Sea port of Novorossiysk, 1,510 kilometres long, with design capacity of 1.6 million barrels per day, in commercial operation since 2001. CPC carries the majority of Tengiz, Karachaganak, and Kashagan production. CPC is the principal Russia-routed export route for Caspian crude and has periodically been disrupted by political tensions, weather events, and operational issues at the Novorossiysk loading terminal.

The Trans-Anatolian Pipeline (TANAP) and the Trans-Adriatic Pipeline (TAP) together form the Southern Gas Corridor for Caspian gas exports to Europe. TANAP runs from the Georgian-Turkish border across Türkiye to the Greek border; TAP runs from the Greek-Turkish border across Greece and Albania under the Adriatic Sea to southern Italy. The combined Southern Gas Corridor became fully operational in late 2020 and has a current capacity of approximately 16 billion cubic metres per year. The long-discussed trans-Caspian gas pipeline from Turkmenistan to Azerbaijan, which would route Turkmen gas to European markets via the Southern Gas Corridor, has been under active negotiations since 2022, and the EIA Protocol, ratified by all five littoral states once Iran ratified on 30 July 2025, will provide the formal procedural framework for its transboundary environmental assessment once that protocol formally enters into force.

Beluga sturgeon: ~90% of world wild caviar historically; CITES II, critically endangered

The beluga sturgeon (Huso huso) is the largest of the Caspian sturgeon species and the source of beluga caviar, historically the most prized variety globally. The species can reach lengths of more than 6 metres and weights of more than 1,000 kilograms, with the largest individuals being slow-growing fish more than 50 years old. The Caspian historically supplied approximately 90 percent of the world’s wild caviar production, with the bulk from beluga, Russian sturgeon (Acipenser gueldenstaedtii), Persian sturgeon (Acipenser persicus), and stellate sturgeon (Acipenser stellatus).

The Caspian sturgeon stocks collapsed catastrophically over the 1990s and 2000s. Wild beluga populations declined by more than 90 percent from the 1980s baseline. The collapse was driven by the combined effects of poaching during the chaotic post-Soviet decade (when enforcement of the historical Soviet-era closed-fishing regime collapsed), habitat degradation in the Volga and Ural spawning rivers from dam construction blocking migration to historical spawning grounds, pollution loading from the Volga catchment (heavy metals and persistent organic pollutants accumulating in long-lived sturgeon tissues), and the cumulative impact of the 1999 Mnemiopsis leidyi invasion.

The CITES regime has progressively tightened international trade in Caspian sturgeon products. All Caspian sturgeon species were listed in CITES Appendix II in 1998, requiring export permits for international trade. CITES imposed zero quotas on wild beluga caviar exports from all Caspian range states for several years in the 2000s, and re-introduction of small quotas was made conditional on national stock-management plans. In January 2006 CITES suspended trading of all wild beluga sturgeon caviar from the Caspian. Wild beluga caviar exports remain severely constrained; most international trade is now in farmed sturgeon products from Italy, France, Iran, China, and the United States. The Tehran Convention regime, the Ashgabat Biodiversity Protocol (once in force), and the parallel Commission on Aquatic Bioresources of the Caspian Sea (CABCS), established by the 2014 Astana Agreement, are the principal regional instruments for sturgeon conservation.

Caspian seal (Pusa caspica): only marine mammal, IUCN Endangered since 2008

The Caspian seal (Pusa caspica) is the only marine mammal native to the Caspian Sea and one of only two pinniped species native to enclosed water bodies globally (the other being the Baikal seal, Pusa sibirica). The species is a small phocid seal closely related to the Arctic ringed seal, evolutionarily isolated in the Caspian since the Pleistocene when the basin was last connected to the proto-Arctic system. It is endemic to the Caspian and has no natural range outside the basin.

The IUCN Red List currently estimates the total population at approximately 104,000 to 168,000 individuals, including approximately 68,000 reproductively mature individuals, with a maximum annual pup production of approximately 34,000. This represents approximately 70 to 80 percent decline from the 1960s baseline of 500,000 to 600,000 and approximately 90 percent decline from the estimated 1 million individuals in 1900. The species was reclassified from “Vulnerable” to “Endangered” on the IUCN Red List in 2008 and has remained in that category since.

The decline drivers include historical commercial hunting (largely terminated by 2010 under successive moratoria and formal hunting bans, though an estimated 18,000 seals are still legally killed annually for fur and blubber by some littoral states), high persistent-organic-pollutant burden in body tissues (PCBs and organochlorine pesticides accumulated through the top-predator position in the food web), reduced kilka prey base following the 1999 Mnemiopsis invasion, reduced ice cover in the Northern Caspian (where seals breed and pup on seasonal sea ice, and declining ice cover has reduced available pupping habitat), and bycatch in fisheries. The Caspian seal is a Bonn Convention (CMS) Appendix II species since 2007 and is the subject of the Caspian Seal Conservation Action Plan. Its population status is a primary indicator of the basin’s overall ecosystem health.

Mnemiopsis leidyi invasion (1999) + kilka fishery collapse

In 1999 the comb jelly Mnemiopsis leidyi was confirmed in the Caspian Sea, having been transported from the Black Sea (where it had invaded in the early 1980s) through ballast water on cargo vessels transiting the Volga-Don canal system. The Caspian invasion was a textbook secondary invasion: the species had already devastated the Black Sea anchovy fishery, and its arrival in the Caspian was widely anticipated by fisheries scientists.

The Caspian Mnemiopsis population expanded explosively through the early 2000s. By 2003 the species was distributed throughout the Middle and Southern Caspian (the Northern Caspian’s lower salinities provide only partial buffering). The total Mnemiopsis biomass at peak in 2002-2003 was estimated at approximately 600 million tonnes wet weight, comparable to the 1989 Black Sea peak. The consequences for Caspian fisheries were as catastrophic as the Black Sea precedent. The kilka (Clupeonella spp.) fishery, the historical mainstay of Caspian fisheries by tonnage, collapsed by approximately 80 percent between 1999 and 2004, falling from an annual catch of approximately 250,000 tonnes to less than 50,000 tonnes. The total Caspian fisheries catch fell from approximately 400,000 tonnes per year in the 1990s peak to around 100,000 to 150,000 tonnes per year in the late 2000s.

Without the biological control provided by Beroe ovata (the specialised Mnemiopsis predator that partially controlled the Black Sea population), the Caspian Mnemiopsis population has stabilised at a high baseline and continues to suppress the kilka fishery. The kilka catch in 2024 was approximately 100,000 to 130,000 tonnes per year, a partial recovery from the 2000s low but substantially below the pre-invasion baseline. The cumulative impact on the Caspian seal (which feeds principally on kilka) and on the sturgeon has compounded the long-term decline of these species.

The Mnemiopsis episode is a textbook case in invasive species through ballast water. The Tehran Convention regime cooperates with the IMO Ballast Water Management Convention through informal arrangements, although the Caspian’s non-IMO-jurisdiction status means BWM Convention requirements don’t formally apply to Caspian-flagged vessels.

Sea level decline: ~2m drop 2006-2024 reaching record low

The Caspian Sea level has been declining since the mid-1990s after a pronounced rise during the 1978-1995 period that raised the level by approximately 2.5 metres and caused substantial coastal flooding in the low-lying Northern Caspian. The cumulative loss from 2006 to 2024 has been approximately 2 metres, with the sea reaching its lowest recorded level of approximately -29 metres relative to the world ocean datum. NASA satellite altimetry (TOPEX/Poseidon, Jason-series, Sentinel-3) documents the decline rate at approximately 7 centimetres per year through 2020, accelerating to 20 to 30 centimetres per year in some measurements since 2020.

The decline drivers are dominated by increased basin-wide evaporation under rising air temperatures (accounting for an estimated 50 to 60 percent of the imbalance), reduced Volga inflow due to upstream water management and climate-driven precipitation changes (approximately 20 to 30 percent), and reduced precipitation across the Caspian catchment (approximately 15 to 25 percent). Increased water loss to the Kara-Bogaz-Gol lagoon accounts for the remainder.

The ecological and economic consequences are substantial. The Volga delta wetlands have lost approximately 5 to 10 percent of their inundated area, with implications for fish nursery and migratory bird habitat. Coastal port infrastructure has been progressively stranded, requiring extensive dredging at Aktau, Atyrau, and other ports. More than 7,000 km² of water area have been lost relative to 2001, with the coast regressing by more than 56 kilometres in some areas. The 2030 outlook is for continued decline, with the cumulative loss potentially reaching 1.5 to 2.0 metres below the 2006 baseline by 2050 under current climate trajectories. Climate adaptation is on the Tehran Convention COP-7 agenda.

Volga pollution: 60 million catchment inhabitants

The Volga catchment is the dominant source of pollution loads to the Caspian. The catchment population of approximately 60 million inhabitants, the approximately 45 percent share of Russian industrial production, and the approximately 50 percent share of Russian agricultural production combine to deliver an enormous pollution load to the basin’s northern entry point. The principal pollution categories are nutrients (annual loads of approximately 800,000 tonnes of nitrogen and 50,000 tonnes of phosphorus), persistent organic pollutants (PCBs, organochlorine pesticides DDT and lindane, polycyclic aromatic hydrocarbons), heavy metals from mining and metallurgical industries especially in the upper Kama and Volga catchments, oil hydrocarbons from upstream petroleum production and refining, radionuclides from past Soviet nuclear activities and Chernobyl, and emerging contaminants including pharmaceuticals, personal care products, and microplastics.

The cumulative load from the Volga is estimated at approximately 70 to 75 percent of the total Caspian pollution input, dwarfing contributions from other rivers and from direct coastal sources. The Tehran Convention’s Moscow Protocol on Land-Based Sources is therefore primarily a Volga-management instrument in operational practice, even though it is formally a basin-wide instrument applicable to all five littoral states. Russian implementation commitments under the Moscow Protocol are delivered through the Volga Federal Programme and coordinated reporting to the Tehran Convention Secretariat.

Caspian outside MARPOL: patchwork voluntary application

The Caspian Sea is outside the geographic scope of MARPOL 73/78 in operational practice. MARPOL applies to ships operating “at sea,” and the Caspian is not a sea under the 2018 Legal Status Convention formula (which characterises it as a body of water with “special legal status”), nor is it a sea under UNCLOS in the conventional sense. The IMO has consistently held that the Caspian is outside its regulatory purview, and Caspian-flagged vessels operating exclusively within the basin aren’t subject to MARPOL flag-state obligations.

The five Caspian littoral states have varied IMO accession profiles for the principal MARPOL Annexes. Russia is a Party to all six MARPOL Annexes and applies them to its world-ocean fleet, but its Caspian fleet operates under Russian federal environmental law that incorporates MARPOL standards voluntarily for the larger vessels. Iran is a Party to MARPOL Annexes I, II, III, and V, applies MARPOL standards to its Persian Gulf fleet, and applies most MARPOL standards to its Caspian fleet voluntarily. Azerbaijan, Kazakhstan, and Turkmenistan are Parties to varying subsets of the MARPOL Annexes and apply MARPOL standards to their Caspian fleets at their discretion.

The result is a patchwork application of MARPOL-equivalent standards across the Caspian fleet, with no central enforcement and no flag-state-port-state regime equivalent to the global MARPOL machinery. The Tehran Convention’s Aktau Protocol on oil pollution response and the Moscow Protocol on land-based sources are the principal binding regional instruments that fill the MARPOL gap, though their substantive standards are framed at the regional cooperation level and don’t include the detailed discharge-criteria architecture of the MARPOL Annexes.

The Caspian is also outside the global OPRC 1990 instrument’s operational scope (the Aktau Protocol replicates many OPRC obligations regionally), outside the CLC 1992 civil-liability regime (though the Caspian states apply civil-liability standards through national law), outside the Bunker Convention 2001 mandatory bunker-spill insurance regime, and outside the Ballast Water Management Convention 2004 machinery (though the Caspian states have implemented ballast water management standards through national legislation, partly motivated by the Mnemiopsis leidyi invasion of 1999).

Absence of MARPOL Special Areas + PSSAs

The Caspian Sea has no MARPOL Special Areas under any of Annexes I, II, IV, V, or VI, and no IMO Particularly Sensitive Sea Area (PSSA) designation, in stark contrast to the Helsinki Convention Baltic Sea (Annex I and V Special Areas, Annex VI SECA and NECA), the Bucharest Convention Black Sea (Annex I and V Special Areas), the Barcelona Convention Mediterranean (Annex I and V Special Areas, Annex VI SECA from 2025), and the Kuwait Convention Persian Gulf (Annex I and V Special Areas).

The absence of MARPOL Special Areas in the Caspian is a direct consequence of the basin’s exclusion from the IMO regulatory scope. A Special Area designation under MARPOL requires the IMO Marine Environment Protection Committee to act under MARPOL Article 16, which requires the area to be a “sea area” within the meaning of MARPOL; the IMO has consistently held that the Caspian doesn’t qualify. The same logic applies to the absence of PSSA designations: PSSA designation under the IMO’s PSSA Guidelines requires MEPC action, and the IMO doesn’t exercise jurisdiction over the Caspian.

Some Caspian-region environmental advocates have proposed that the Tehran Convention regime should establish its own equivalent of MARPOL Special Areas at the regional level, potentially through an additional Protocol or amendments to the 2012 Moscow Protocol, but no such initiative has gained sufficient Contracting Party support as of 2026.

2030 outlook: TITR transit corridor + climate + legal status ratification

The 2030 outlook for the Tehran Convention regime is shaped by three principal forces: the growth of the Trans-Caspian International Transport Route (TITR / Middle Corridor), the climate-driven sea level decline and its ecosystem consequences, and the pending ratification of the 2018 Legal Status Convention by Iran.

The TITR / Middle Corridor is the multimodal transit route connecting China to Europe through Kazakhstan, the Caspian Sea, Azerbaijan, Georgia, and Türkiye, bypassing the historical Russian transit. The corridor grew rapidly after 2022 as European importers sought non-Russian routes, with freight volumes rising approximately 70 percent in 2024 to approximately 4 to 4.5 million tonnes for the year and container shipments increasing 2.6-fold to approximately 50,500 TEU in the first eleven months of 2024. Projections to 2027 suggest Middle Corridor capacity could reach 10 million tonnes per year. The Caspian crossing component (Aktau to Baku, or Turkmenbashi to Baku) is the bottleneck of the route, with major infrastructure investments underway at Aktau, Kuryk, Turkmenbashi, and Baku ports. Rising vessel traffic has direct implications for the Tehran Convention regime’s spill-response capacity, vessel discharge regulation, and cumulative emissions impact.

The climate-driven sea level decline is expected to continue through 2030, with cumulative loss potentially reaching 1.5 metres below the 2006 baseline. The Tehran Convention COP-7 agenda includes a climate adaptation package addressing port-infrastructure stranding, wetland habitat loss in the Volga delta, sturgeon spawning habitat compression, and Caspian seal ice-cover loss.

Iran’s ratification of the 2018 Legal Status Convention is the key political variable for 2026. A Caspian Summit in Tehran is expected in August 2026, at which Iranian ratification could be addressed. Iran’s ratification of the EIA Protocol on 30 July 2025, completing all five littoral ratifications of that protocol, suggests the broader political environment may be moving toward Legal Status Convention ratification.

Comparison to Kuwait Convention 1978 (Iran in both)

The Kuwait Convention 1978 (formally the Kuwait Regional Convention for Cooperation on the Protection of the Marine Environment from Pollution) is the regional sea convention for the Persian Gulf, the Gulf of Oman, and the wider ROPME Sea Area, with eight Contracting Parties including Iran. Iran is therefore a Contracting Party to both the Tehran Convention (Caspian) and the Kuwait Convention (Persian Gulf), making the comparison particularly informative.

The structural parallels are direct: both Conventions are framework instruments supplemented by thematic Protocols, both have Permanent Secretariats, both are governed by Conferences of Contracting Parties, both are within the UNEP Regional Seas Programme, and both address dual land-based and maritime pollution across semi-enclosed or enclosed water bodies with intense hydrocarbon activity.

The differences are substantial, as summarised below.

The Iranian implementation profile across the two regimes is informative. Iran applies a generally cooperative approach to ROPME under the Kuwait Convention, including support for the parallel MEMAC (Marine Emergency Mutual Aid Centre) regional response architecture in the Persian Gulf. In the Caspian, Iran has applied a similarly cooperative approach under the Tehran Convention, with active participation in the COP machinery and in the Aktau Protocol’s regional response operations.

Comparison to Helsinki Convention 1992 (parallel semi-enclosed basin)

The Helsinki Convention 1992 (HELCOM) is the most direct structural analogue to the Tehran Convention: both cover enclosed or semi-enclosed inland-feel water bodies with severe pollution legacies, climate-driven hydrographic changes, and complex multi-state riparian configurations.

The differences are equally significant.

The two Conventions cooperate informally through the UNEP Regional Seas Programme, with joint workshops addressing brackish-water marine ecology, climate-driven sea level changes (rising in the Baltic, falling in the Caspian), and ballast-water-mediated invasive species relevant to both basins.

Comparison to Bucharest Convention 1992 (closest geographic neighbour)

The Bucharest Convention 1992 is the closest geographic neighbour, covering the Black Sea immediately west of the Caspian basin. The two regimes share the same general regional context (post-Soviet riparian states, Volga-Don catchment hydrologic links, common Mnemiopsis leidyi invasion, Russian and Iranian connections).

The two regimes interact through several channels. The Volga-Don shipping canal physically connects the Caspian to the Sea of Azov / Black Sea system and is the principal vector for the Mnemiopsis invasion that affected both basins. The CPC pipeline routes Kazakhstani crude from the Caspian to the Russian Black Sea coast. The Russian Federation is a Contracting Party to both Conventions, and its Caspian-Black Sea fleet operates across both regimes. The two Secretariats have held bilateral cooperation meetings since the late 2010s, particularly on Mnemiopsis monitoring and on the Russian implementation profile across the two regimes.

Regulatory profile for Caspian fleet operators

A practical summary for vessel operators: a Caspian product tanker on a round voyage from Aktau (Kazakhstan) to Baku (Azerbaijan) and return faces the following regulatory environment as of 2026.

MARPOL does not formally apply to Caspian-flagged vessels operating exclusively within the basin. There is no Annex I, II, IV, V, or VI flag-state-port-state regime equivalent to the global MARPOL machinery. The operator must rely on flag-state national environmental law (Kazakhstan or Azerbaijan in this case) for discharge standards.

Tehran Convention regime applies through the national environmental law of the flag state and the port state, cross-referencing the Aktau Protocol on Oil Pollution Response and the Moscow Protocol on Land-Based Sources. Under the Aktau Protocol’s response architecture, a spill incident requires notification of the flag-state competent authority and the port-state competent authority; the regional activity centre coordinates joint response if the spill exceeds national capacity; and pre-positioned response equipment is available at major ports. No CLC 1992 mandatory civil-liability cover is required by the IMO regime, though flag states may impose national civil-liability insurance requirements. No mandatory MARPOL Annex I oil record book is required by the IMO regime, though flag states typically require equivalent national record-keeping. No SECA or NECA applies in the Caspian; bunker fuel sulphur compliance is at the global 0.50 percent cap level if the vessel imports bunkers from a MARPOL Annex VI Party, or at the national-law standard of the flag and bunker-supply state otherwise.

New projects (offshore platforms, pipelines, ports) will fall under the EIA Protocol once it formally enters into force, requiring transboundary environmental impact assessment notified to all five Parties before authorisation. All five littoral states have ratified the protocol (Iran on 30 July 2025), but the Secretariat has not yet published an entry-into-force date, so operators should track the protocol’s status rather than assume it is already binding.

Three common errors recur in trade-press and operator-side communication. First, assuming MARPOL applies to Caspian-flagged vessels: it doesn’t formally; Caspian fleet compliance with MARPOL-equivalent standards is voluntary at flag-state discretion. Second, conflating the 2018 Aktau Convention on Legal Status with the 2011 Aktau Protocol on Oil Pollution Response: these are distinct instruments adopted at distinct Aktau summits seven years apart. Third, assuming the Caspian is a MARPOL Special Area: the Caspian has no MARPOL Special Area, SECA, NECA, or PSSA designation as of 2026.

See also

• MARPOL Convention
• MARPOL Annex I oil pollution prevention
• Kuwait Convention 1978
• Jeddah Convention 1982
• Abidjan Convention 1981
• Nairobi Convention 1985
• Helsinki Convention 1992
• Bucharest Convention 1992
• Barcelona Convention 1976-1995
• OSPAR Convention 1992
• PSSA overview
• Ballast Water Management Convention
• IMO 2020 sulphur cap
• UNEP Regional Seas Programme
• Calculators