Regulatory performance assessment of alternative marine fuels to decarbonize ocean-going vessels

The maritime industry faces increasing pressure to decarbonize ocean-going vessels to meet the International Maritime Organization’s emissions targets. This study evaluates the regulatory compliance of three alternative marine fuels, liquified natural gas (LNG), liquified petroleum gas (LPG) and methanol, through evaluating the Energy Efficiency Existing Ship Index (EEXI) and Carbon Intensity Indicator (CII) for three vessel types: a container ship, bulk carrier, and tanker. Using a structured regulatory framework, attained EEXI and CII values under each fuel scenario were calculated and compared to IMO requirements. The results indicate a clear performance hierarchy; LNG dual-fuel engines achieved full compliance across both regulatory metrics, reducing attained EEXI by 17%–25% compared to conventional fuels and maintaining A or B ratings for CII through 2025–2030. LPG fulfilled the EEXI requirement only for the bulk carrier and showed marginal CII compliance due to its high carbon conversion factor. Methanol failed to meet EEXI limits in all three cases, exceeding requirements by 2%–41% and yielded the lowest CII ratings compared to other fuels, primarily due to its low energy density. LNG emerges as the most viable short-term compliance solution among the fuels considered.