Well-to-Wake (WtW)

Well-to-wake (WtW) is the lifecycle greenhouse gas accounting basis that counts emissions from fuel extraction and production (well-to-tank) plus combustion and slip on board (tank-to-wake). It is the basis for the greenhouse gas fuel intensity (GFI) metric in the IMO Net-Zero Framework’s draft MARPOL Annex VI Chapter 5 and is set out in the IMO lifecycle GHG assessment guidelines, MEPC.391(81). WtW captures the upstream emissions and the methane and nitrous oxide slip that a tank-to-wake or CII tailpipe metric misses, which is why a fuel like LNG or grey hydrogen can look cleaner at the funnel yet score worse on a WtW basis. The EU FuelEU Maritime intensity target uses the same WtW principle.