Extended Operational and Trade Vocabulary

Decarbonization, Alternative Fuels and Carbon Pricing glossary

The decarbonization and carbon-pricing vocabulary: the CII rating bands under MEPC.336(76), abatement cost per tonne of CO2eq, onboard carbon capture with amine absorbents, acceptable fuel pathways under FuelEU Maritime and the IMO LCA framework, and the sustainability class notations. Grounds each term in the efficiency regulation or the fuel-certification scheme it belongs to.

318 defined terms.

Showing 250 on this page (page 1 of 2).

A

A rating (CII): Top Carbon Intensity Indicator band under MEPC.336(76), denoting major superior performance versus the required AER reference line.
Abatement Cost: Cost per ton of emissions avoided.
ABS Sustainability Notations: American Bureau of Shipping class notations covering GHG, CII readiness, and decarbonization readiness, including the Carbon Smart Fleet (CSF) program.
Absorbent (amine): Liquid solvent such as MEA used in post-combustion CO2 capture aboard ships.
Acceptable fuel pathway: Production route certified as meeting GHG intensity criteria under FuelEU Maritime or the IMO LCA framework.
Accredited verifier: Body accredited to ISO 14065 or ISO 17029 authorized to verify EU MRV, EU ETS, and FuelEU Maritime data.
AER (Annual Efficiency Ratio): Carbon intensity metric used in early shipping efficiency reporting.
Aframax efficiency baseline: EEDI reference line value applied to Aframax crude tankers under MARPOL Annex VI Chapter 4.
Air Lubrication System (ALS): System reducing hull friction via injected air bubbles.
Airseas Seawing: Automated parafoil kite wind-assist system developed by Airseas (Airbus spinoff).
Alcohol-to-Jet (ATJ): Synthetic fuel pathway producing hydrocarbons from alcohols; relevant as a feedstock route for marine drop-in fuels.
Alkaline electrolyzer: Mature electrolysis technology used to produce green hydrogen feedstock for e-fuels.
Allowance (EUA): EU Emissions Trading System unit equal to 1 tonne of CO2 equivalent.
Ambition (IMO): Quantified GHG reduction target in the IMO Revised Strategy MEPC.377(80): net-zero by or around 2050, with 2030 and 2040 checkpoints.
Amine scrubbing: Post-combustion CO2 capture using monoethanolamine (MEA) or proprietary solvents.
Ammonia (NH3): Carbon-free fuel candidate; combustion produces no CO2 but raises NOx and N2O concerns and requires SCR aftertreatment.
Ammonia bunkering: Ship-to-ship or shore-to-ship transfer of liquid ammonia at approximately minus 33 C atmospheric pressure or semi-refrigerated.
Ammonia cracker: Onboard unit decomposing NH3 to H2 + N2 for fuel cell feed.
Ammonia slip: Unburned NH3 emitted from engines and SCR systems, regulated for toxicity and N2O formation.
AMP (Alternative Maritime Power): Shore-supplied electrical power to a berthed ship, also called cold ironing or OPS.
Anaerobic digestion: Biological process producing biogas (CH4 + CO2) upgradable to bio-LNG.
Anemoi rotor sail: Flettner rotor wind-assist product line by Anemoi Marine Technologies.
AR6 (IPCC Sixth Assessment Report): Source of current GWP values used in maritime GHG accounting.
Aramis project: Dutch CO2 transport and storage initiative led by EBN, Gasunie, Shell, and TotalEnergies.
Article 18 fund (FuelEU): Provision for pooling and banking of GHG intensity compliance balances.
Auction (EUA): Primary market sale of EU allowances on EEX, the EU's common auction platform.
Australia-Japan iron ore green corridor: Announced ammonia-fueled bulk carrier route under the Clydebank Declaration framework.
Avoided emissions: Emissions not released due to a mitigation measure, distinct from removals.

B

B24, B30, B100: Biodiesel blends containing 24%, 30%, and 100% FAME respectively.
Banking (FuelEU): Carrying surplus GHG intensity compliance from one year to subsequent years.
BAR Technologies WindWings: Solid wing sail wind-assist system installed on Cargill chartered Pyxis Ocean (2023).
Baseline (2008): Reference year for IMO GHG reduction percentages under MEPC.304(72) and MEPC.377(80).
Battery-electric vessel: Ship powered solely by onboard lithium-ion batteries; common on short-route ferries.
BECCS: Bioenergy with carbon capture and storage; combines biofuel use with CO2 capture for net-negative emissions accounting.
Berth emissions: GHGs released while a ship is at berth; fully covered under EU ETS Maritime from 2024.
Bio-LNG: Liquefied biomethane used as drop-in fuel for LNG ships.
Bio-methanol: Methanol produced from sustainable biomass feedstocks via gasification and synthesis.
Biofuel: Liquid or gaseous fuel from biomass; covered by ISCC EU or RED II certification for FuelEU.
Biogenic CO2: Carbon dioxide originating from biomass; treated as zero in tank-to-wake accounting but counted in well-to-tank.
Blue Ammonia: Ammonia produced from natural gas with CCS.
Blue Hydrogen: Hydrogen from fossil sources combined with carbon capture and storage.
Blue methanol: Methanol from natural gas with CCS on the production process.
BlueAngel: German voluntary environmental label including a ship-design sub-scheme.
BOG (Boil-Off Gas): Vapor evolving from cryogenic LNG, LH2, or NH3 tanks; managed by re-liquefaction, combustion, or reuse as fuel.
Bottom fouling: Marine growth on the hull that increases frictional resistance and fuel consumption.
BTL (Biomass-to-Liquid): Pathway producing synthetic diesel from biomass via gasification and Fischer-Tropsch synthesis.
Bunker Delivery Note (BDN): Required under MARPOL Annex VI Regulation 18.
Bureau Veritas Decarb Ready: BV class notation marking ship readiness for future fuel conversion.

C

C rating (CII): Middle CII performance band under MEPC.336(76); no corrective action required.
Calcium looping: High-temperature CO2 capture process using CaO/CaCO3 cycle.
CAPEX (Decarbonization): Capital expenditure on fuel-flexible engines, tanks, fuel cells, or wind assist.
Captured CO2: CO2 separated from flue gas, intended for use, transport, or geological storage.
Carbon Border Adjustment Mechanism (CBAM): EU mechanism pricing imported carbon-intensive goods.
Carbon Credit: Tradable unit representing one ton of CO2 equivalent reduced.
Carbon dioxide (CO2): Primary GHG from fossil fuel combustion; GWP-100 = 1 by definition.
Carbon Disclosure Project (CDP): Voluntary corporate climate disclosure framework used by shipping operators.
Carbon intensity: GHG emissions per unit of transport work or energy delivered.
Carbon Intensity Indicator (CII): Operational indicator under MARPOL Annex VI Chapter 4.
Carbon Pricing: Policy assigning a cost to greenhouse gas emissions.
Carbon-neutral fuel: Fuel whose net well-to-wake CO2 emissions are zero on a lifecycle basis.
Cargill ocean transportation: Charterer running early wind-assist (BAR WindWings) and methanol trials.
CCS (Carbon Capture and Storage): Capture of CO2 from a source followed by permanent geological storage.
CCU (Carbon Capture and Utilization): Use of captured CO2 as feedstock for fuels, chemicals, or materials.
CGH2 (Compressed Gaseous Hydrogen): Hydrogen stored at 350 or 700 bar.
CH4 (Methane): Principal component of LNG; GWP-100 of 28 to 30 under IPCC AR6, GWP-20 of around 84.
Charterer claim: Voluntary commitment such as the Sea Cargo Charter requiring disclosure of fleet carbon intensity.
CHEK Horizon project: EU-funded R&D combining wind-assist, hydrogen, and energy-saving technologies on a Wartsila concept ship.
CII reduction factor (Z): Annual tightening factor in the CII formula under MEPC.338(76).
Class society: Recognized Organization issuing IEE, IAPP, and DCS-related certificates on behalf of flag states.
Clean Shipping Index (CSI): Voluntary environmental rating run by the Clean Shipping Network.
Clydebank Declaration for Green Shipping Corridors: Statement signed at COP26 in 2021 by 22 nations to establish at least six zero-emission shipping corridors by 2025.
CO2 capture rate: Share of CO2 in exhaust captured by onboard CCS, typically targeted at 30 to 90 percent.
CO2eq (CO2 equivalent): Common unit combining gases by GWP for aggregate reporting.
Cold Ironing: Onshore power supply enabling ships to shut down engines in port.
Combustion management: Engine control measures reducing methane slip on LNG dual-fuel engines.
Compliance balance (FuelEU): Difference between a ship's attained and target GHG intensity multiplied by total energy used.
Compliance period (FuelEU): Calendar year for which GHG intensity must be calculated and verified.
Composite reference line: Aggregate EEDI baseline used in regulatory phase determination.
Cool-down: Pre-trip lowering of empty container interior to set point before stuffing cargo.
COP26 (Glasgow 2021): UNFCCC conference at which the Clydebank Declaration was signed.
Correction factors (EEDI/EEXI): Adjustments for ice class, voluntary structural enhancements, shuttle tankers, and other ship-specific features under MEPC.364(79).
Corridor (green): Specific trade lane committing to zero or near-zero emission shipping operations.
CORSIA: Aviation offset scheme; cited for comparison with proposed IMO economic measures.
Cross-flow methanol injector: Injector design for low-pressure methanol dual-fuel engines.
Cryocondenser: Cooling device that condenses methane slip or BOG by deep refrigeration.
Cryogenic CO2: CO2 liquefied at low temperature for storage or transport onboard CCS vessels.
CSF (Carbon Smart Fleet): ABS notation program for tracking and reducing fleet GHG intensity.

D

DCS (IMO Data Collection System): Mandatory fuel oil consumption data reporting since 2019.
Decarbonization pathway: Sequence of measures (operational, technical, fuel switch) leading to net-zero emissions.
Deep sea sequestration: Geological storage of CO2 beneath the seabed, e.g. Northern Lights.
Demand-side measure: Reduction of energy demand on board (speed, hull, propeller) before fuel switching.
DIN 51626: German biodiesel standard sometimes referenced in marine biofuel contracts.
Direct Air Capture (DAC): Extraction of CO2 directly from ambient air.
DNV Maritime Forecast to 2050: Annual scenario report on maritime decarbonization.
Drop-in fuel: Bio or synthetic fuel meeting ISO 8217 distillate or residual specifications and usable without engine modification.
Dual-fuel engine: Engine running on both liquid and gaseous fuels (e.g., WinGD X-DF).
Dynamic positioning fuel use: DP operation included in FuelEU and EU MRV scope when associated with covered voyages.

E

e-ammonia: Ammonia synthesized from green hydrogen and air-sourced nitrogen using renewable electricity.
e-diesel: Synthetic distillate from green hydrogen and captured CO2 via Fischer-Tropsch.
e-LNG: Synthetic methane from green hydrogen and captured CO2 via Sabatier process.
E-Methanol: Methanol synthesized from green hydrogen and captured CO2.
E5 (CII): Lowest CII band; ship must include a corrective action plan in SEEMP Part III.
EBN (Energie Beheer Nederland): State-owned Dutch entity, partner in the Aramis CCS project.
Eco-Flettner: Lower-cost Flettner rotor design developed for short-sea vessels.
Econowind Ventifoil: Suction wing wind-assist system using boundary-layer suction; uses the Magnus and thin-airfoil principles.
EEDI (Energy Efficiency Design Index): Mandatory IMO design efficiency metric for new ships.
EEDI Phase 3: Strictest EEDI tier, effective 1 April 2022 for many ship types under MEPC.328(76).
EEOI (Energy Efficiency Operational Indicator): Voluntary IMO operational efficiency metric.
EEX (European Energy Exchange): Exchange offering cleared dry FFA and tanker freight derivatives.
EEXI (Energy Efficiency Existing Ship Index): IMO design efficiency metric for existing ships.
EGR (Exhaust Gas Recirculation): NOx control method per MARPOL Annex VI Tier III.
Electrofuel: See E-Fuel.
Emission Control Area (ECA): Sea area with stricter SOx, NOx, or PM controls.
Emission Factor: Mass of emissions per unit of activity or fuel.
EnergyObserver: Hydrogen and renewables demonstration vessel showcasing PEM fuel cell technology.
Equinor: Norwegian operator and partner in the Northern Lights CO2 storage project.
EROEI: Energy return on energy invested; metric for evaluating alternative fuel pathways.
ESI (Environmental Ship Index): Voluntary scoring system administered by the International Association of Ports and Harbors offering port-dues discounts.
EU Allowance (EUA): Unit of compliance in the EU Emissions Trading System.
EU ETS Maritime: Extension of the EU Emissions Trading System to shipping under Directive 2023/959; applies from 1 January 2024 with phased surrender of 40% in 2024, 70% in 2025, and 100% from 2026.
EU MRV: EU Regulation 2015/757 on monitoring, reporting, and verification of CO2 emissions from shipping.
EU Taxonomy: Classification system identifying shipping activities as environmentally sustainable for finance purposes.
EUA spot price: Daily settlement price for EU allowances on EEX or ICE Endex.
EVDI (Existing Vessel Design Index): RightShip-developed design-stage carbon intensity metric, distinct from EEDI.
EverLoNG: EU-funded project demonstrating onboard CCS on LNG-fueled ships.
Existing ship (EEXI): Any ship not classified as a new ship under MARPOL Annex VI definitions.
External cost: Climate damage cost not internalized in fuel price; basis for economic measures.

F

FAME (Fatty Acid Methyl Ester): Biodiesel component; capped or allowed depending on ISO 8217 edition and grade.
Feebate: Fee-and-rebate carbon pricing structure proposed in some IMO submissions.
FID (Final Investment Decision): Milestone for green fuel production or bunkering infrastructure projects.
Fischer-Tropsch Synthesis: Process converting syngas to liquid hydrocarbons.
Flag administration: Government body responsible for ship registration, certification and oversight of the national fleet.
Flettner rotor: Wind-assisted propulsion using Magnus effect.
FONAR (Fuel Oil Non-Availability Report): Document submitted under MARPOL Annex VI Reg 18.2.4 when compliant fuel cannot be obtained.
Fuel Cell: Device converting fuel and oxidant directly to electricity.
Fuel cell stack: Series of cells producing usable voltage; PEM, SOFC, MCFC variants common in maritime.
Fuel EU Maritime: EU regulation limiting GHG intensity of marine fuels from 2025.
Fuel flexibility: Ability of an engine or vessel design to switch between multiple fuels.
Fuel pathway certification: Verification of feedstock and process route used to derive a fuel's WtW emission factor.
Fuel pool (FuelEU): Mechanism allowing multiple ships to combine compliance balances for one reporting period.

G

Getting to Zero Coalition: Industry alliance hosted by the Global Maritime Forum, Friends of Ocean Action, and the World Economic Forum.
GHG fuel standard: Lifecycle GHG intensity limit on marine fuels, central to the IMO Net-Zero Framework.
GHG Intensity (FuelEU): gCO2eq/MJ metric per FuelEU Maritime.
Global Maritime Forum (GMF): Convener of Getting to Zero, Sea Cargo Charter, and Poseidon Principles secretariats.
Government Pension Fund Global: Norway sovereign wealth fund; investor influence on shipowner decarbonization.
Gray ammonia: Ammonia produced from fossil hydrogen without CCS.
Gray hydrogen: Hydrogen produced from natural gas via SMR without CO2 capture.
Gray methanol: Methanol from fossil natural gas without CCS.
Green Corridor: Shipping route along which zero-emission options are scaled up.
Green Hydrogen: Hydrogen produced via electrolysis using renewable electricity.
Green Methanol: Methanol produced from renewable feedstocks.
GreenAward: Voluntary certification offering port-dues incentives for high-performing ships.
Greensand project: Danish CO2 storage project in the depleted Nini oil field led by INEOS and Wintershall.
GWP (Global Warming Potential): Relative warming effect of a gas over 20 or 100 years compared with CO2; AR6 values are the IMO LCA reference.
GWP-100: 100-year GWP; methane value approximately 28 to 30, N2O approximately 265, under AR6.
GWP-20: 20-year GWP; methane value approximately 84 under AR6.

H

H2 (Hydrogen): Lightest element; carbon-free fuel candidate stored as LH2 or CGH2.
Haber-Bosch synthesis: Industrial process combining H2 and N2 to make ammonia.
Hard-to-abate sector: Industry segment, including international shipping, where decarbonization is technically and economically difficult.
Heavy fuel oil (HFO): Residual marine fuel, RMG 380, ISO 8217.
High pressure dual-fuel (HPDF): Engine category including MAN ME-GI; reduces methane slip versus low-pressure designs.
High Seas (UNCLOS): Area beyond national jurisdiction; emissions from voyages to or from EU ports counted at 50% under EU ETS.
HVO (Hydrotreated Vegetable Oil): Renewable diesel produced by hydroprocessing fats and oils, fully compatible with conventional distillate systems.
Hydrogen carrier: Substance such as ammonia, methanol, or LOHC used to transport hydrogen.
Hydrogen embrittlement: Material degradation in pipes and tanks exposed to hydrogen.

I

IBIA (International Bunker Industry Association): Trade body active in IMO MEPC submissions on fuel standards.
ICE Endex: Exchange where EUA futures are actively traded.
ICS (International Chamber of Shipping): Trade association proposing market-based measures at IMO.
IEA Net Zero by 2050: International Energy Agency scenario informing maritime decarbonization analysis.
IEE Certificate: International Energy Efficiency Certificate issued under MARPOL Annex VI regulation 8 and required by EEDI, EEXI, and SEEMP.
IGC Code: International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk.
IGF Code: International Code of Safety for Ships Using Gases or Other Low-Flashpoint Fuels.
IMO 2020: 0.50% sulfur cap on marine fuels; not a GHG measure but driving fuel mix changes.
IMO Initial Strategy 2018: Resolution MEPC.304(72) setting reduction goals of at least 40% by 2030 and 50% by 2050 versus 2008.
IMO LCA Guidelines: Resolution MEPC.376(80) on lifecycle GHG intensity of marine fuels using WtW, WtT, and TtW boundaries.
IMO Net-Zero Framework (NZF): Set of mid-term measures adopted at MEPC 83 (April 2025) combining a GHG fuel standard and an economic element.
IMO Revised Strategy 2023: Resolution MEPC.377(80) adopted July 2023; strengthens ambition to net-zero by or around 2050 with checkpoints of 20% (striving 30%) by 2030 and 70% (striving 80%) by 2040 versus 2008.
Indirect land use change (ILUC): Land conversion driven by biofuel demand; affects WtT emission factors under RED II.
INEOS Greensand: Lead operator of the Danish Greensand CO2 storage project.
Initial Strategy (IMO): See IMO Initial Strategy 2018.
Intra-EU voyage: Voyage between two EU ports; 100% of CO2 included in EU ETS Maritime.
ISO 14064: GHG quantification and verification standard.
ISO 14065: Accreditation standard for GHG verification bodies.
ISO 17029: Conformity assessment standard for validation and verification bodies.
ISO 8217: International standard for marine fuel oil specifications.
Iso-conditions: Reference ambient conditions used in EEDI verification.
ITF Shipping Decarbonization Outlook: OECD International Transport Forum scenarios for maritime GHG reductions.

J

JIT (Just-In-Time arrival): Operational practice of adjusting speed for direct berthing, reducing port-area emissions.

K

K2CO3 (potassium carbonate): Solvent used in some CO2 capture pilots, including Hot Potassium Carbonate processes.
Kite propulsion: Wind-assist using a high-altitude towing kite, as in Airseas Seawing and earlier SkySails.
Kyoto Protocol: 1997 UNFCCC instrument predating IMO maritime GHG measures.

L

LCA (Life Cycle Assessment): WtW analysis of GHG emissions covering production, distribution, and use of a fuel.
LCO2 (Liquid CO2): Liquefied carbon dioxide carried in IGC Code Type C tanks at low temperature and moderate pressure.
LCO2 carrier: Vessel transporting liquefied CO2 from capture sites to offshore storage; e.g. Northern Lights shuttles.
LFP (Lithium Iron Phosphate): Battery chemistry common in maritime ESS due to thermal stability.
LH2 (Liquid Hydrogen): Hydrogen liquefied at approximately minus 253 C; demonstrated by Suiso Frontier (Kawasaki).
Lifecycle GHG intensity: WtW emissions per unit of fuel energy, calculated under MEPC.376(80) for IMO and Annex II of FuelEU Maritime for the EU.
LNG (Liquefied Natural Gas): Methane-dominant fuel liquefied at approximately minus 162 C; typical WtW reduction of 15 to 20 percent versus HFO is offset by methane slip.
LNG Bunkering: Process of supplying liquefied natural gas as marine fuel.
LOHC (Liquid Organic Hydrogen Carrier): Compounds such as dibenzyltoluene used to transport hydrogen.
Low-pressure dual fuel (LPDF): Otto-cycle gas engine like Wartsila 31DF.
LSFO (Low Sulfur Fuel Oil): 0.50% sulfur compliant residual fuel; similar GHG intensity to HFO.
LSMGO (Low Sulfur Marine Gas Oil): Distillate marine fuel commonly used inside ECAs.

M

MACC (Marginal Abatement Cost Curve): Ranking of mitigation measures by cost per tonne CO2eq avoided.
Magnus effect: Aerodynamic force on a spinning cylinder in cross-flow, exploited by Flettner rotors.
MAN ME-GA: MAN Energy Solutions two-stroke ammonia-capable dual-fuel engine.
MAN ME-GI: Two-stroke high-pressure (around 300 bar) gas-injection diesel engine by MAN Energy Solutions, Diesel cycle.
MAN ME-LGIA: Two-stroke dual-fuel ammonia engine; prototype demonstrated 2024.
MAN ME-LGIM: Methanol variant of ME-GI for methanol-fueled ships; not LNG but related dual-fuel platform.
MarinE-CCS: Norwegian research initiative on shipboard CO2 capture.
Maritime Just Transition Task Force: Joint effort by ICS, ITF, IMO, ILO, and UN Global Compact addressing seafarer training for alternative fuels.
MARPOL Annex VI: Air pollution and energy-efficiency annex.
MARPOL Annex VI Chapter 4: Energy efficiency provisions including EEDI and SEEMP.
MCFC (Molten Carbonate Fuel Cell): High-temperature fuel cell suitable for combined heat and power; tested on cruise ships.
MEA (Monoethanolamine): Standard amine solvent for post-combustion CO2 capture.
MEPC Marine Environment Protection Committee: IMO committee adopting HKC implementing guidelines.
MEPC.1/Circ.684: Guidelines for voluntary use of the Energy Efficiency Operational Indicator (EEOI).
MEPC.304(72): IMO Initial Strategy on Reduction of GHG Emissions from Ships (2018).
MEPC.328(76): Adoption of MARPOL Annex VI amendments establishing EEXI, CII rating, and enhanced SEEMP.
MEPC.336(76): 2021 Guidelines on operational carbon intensity indicators and the calculation methods.
MEPC.338(76): 2021 Guidelines on the reference lines for use with operational carbon intensity indicators.
MEPC.376(80): IMO guidelines on lifecycle GHG intensity of marine fuels (LCA).
MEPC.377(80): IMO 2023 Revised Strategy on Reduction of GHG Emissions from Ships.
Methane (CH4): Principal LNG component; potent GHG with GWP-100 of 28 to 30 under AR6.
Methane Slip: Unburned methane emissions from dual-fuel LNG engines.
Methanol (CH3OH): Liquid fuel with low flashpoint; gray, blue, bio, and e-pathways exist.
Methanol Institute: Industry body publishing safe handling and bunkering guidance for methanol.
Mission Innovation: International initiative supporting Zero-Emission Shipping Mission and green corridors.
Mitsubishi MOLCCUS: Joint Mitsubishi Shipbuilding and MOL onboard CCS demonstration program.
Monitoring plan (EU MRV): Vessel-specific document approved by the verifier describing data collection methods.

N

N2O (Nitrous oxide): Greenhouse gas with GWP-100 of 265 under AR6; emitted from ammonia combustion and SCR.
Net-zero by or around 2050: Long-term goal in IMO Resolution MEPC.377(80).
Net-Zero Framework (NZF): IMO basket of measures adopted at MEPC 83 in April 2025 combining a GHG fuel standard and an economic element.
New ship (EEDI): Ship with a building contract on or after 1 January 2013, or other defined milestones.
NH3 (Ammonia): Carbon-free fuel with toxicity and N2O concerns.
Non-EU port: Port outside the EU/EEA; voyages to or from such ports counted at 50% under EU ETS Maritime.
Norsepower Rotor Sail: Commercial Flettner rotor product fitted on vessels of Maersk Tankers, Sea-Cargo, and Vale.
Northern Lights: Norwegian CO2 transport and storage joint venture by Equinor, Shell, and TotalEnergies; first phase operational 2024.
NOx Tier III: MARPOL Annex VI NOx limit applying in NOx ECAs; relevant for SCR-equipped alt-fuel engines.
NZF compliance unit: Tradable unit anticipated under the IMO Net-Zero Framework, subject to finalization at MEPC.

O

OPEX (Decarbonization): Operating cost of alternative fuels and abatement technologies.
OPS (Onshore Power Supply): Shore power connection enabling main and auxiliary engine shutdown at berth.
OSV (Offshore Support Vessel): Vessel type with growing battery-hybrid and methanol uptake.
Otto cycle: Combustion cycle used by low-pressure LNG dual-fuel engines, associated with methane slip.

P

Pathway certification: ISCC EU or REDcert process verifying that a fuel meets sustainability criteria.
PEM (Proton Exchange Membrane): Low-temperature hydrogen fuel cell suitable for marine auxiliary or propulsion.
Penalty (FuelEU): 2,400 euro per tonne VLSFO-energy-equivalent of GHG intensity non-compliance under Article 23.
Phase 0/1/2/3 (EEDI): Progressive tightening tiers under MARPOL Annex VI regulation 21.
Pilot Fuel: Small amount of conventional fuel igniting alternative fuel in dual-fuel engines.
Poseidon Principles: Framework for integrating climate considerations into ship finance.