The maritime industry is responsible for the emission of ∼940 million tonnes of CO2 on an annual basis

accounting for roughly 2.9% of the total global anthropogenic greenhouse gas emissions. Achieving the decarbonization objectives set forth by the International Maritime Organization for the years 2030 and 2050 requires an expedited transition towards low-carbon marine fuel alternatives. This review presents a concentrated and quantitative assessment of biodiesel and biodiesel–alcohol blends as viable near-drop-in substitutes for marine gas oil. Non-edible feedstocks

including Jatropha curcas

Pongamia pinnata

used cooking oil

and microalgae

produce biodiesel with heating values ranging from 37 to 42 MJ kg−1 and cetane numbers between 47 and 58

thereby conforming to ISO 8217 specifications. The incorporation of alcohols

most notably n-butanol

in concentrations of 10–20% enhances atomization and ignition properties

resulting in a reduction of CO and hydrocarbon emissions by 50–60% and particulate matter by as much as 70%

accompanied by a modest increase in NOx emissions of 8–15%. A comprehensive meta-analysis of 18 studies representative of marine conditions has corroborated that blends containing 20% biodiesel and 10%-butanol-20% biodiesel maintain brake thermal efficiency (g = −0.03

P > 0.05) while simultaneously decreasing CO

hydrocarbon

and particulate matter emissions by 16–21%. Lifecycle assessments reveal savings of greenhouse gas emissions ranging from 65 to 85% contingent upon the type of feedstock utilized. At the same time

techno-economic evaluations demonstrate that production costs are competitive with those of marine diesel

particularly when factoring in carbon credits. This review distinctively amalgamates statistical synthesis

insights from lifecycle and techno-economic assessments

and a strategic policy roadmap that aligns with the directives of the International Maritime Organization

the European Union Emissions Trading System

and various Asian maritime frameworks

thereby providing stakeholders with practical guidance for the large-scale implementation and adherence to the objectives of International Maritime Organization Tier III and carbon intensity indicator.