There are currently two separate approaches for estimating global CO2 emissions from marine fishing. One approach uses catch-based fuel use intensity (FUI) estimates for well-studied areas/fisheries to estimate FUI in data poor regions. The second approach, effort-based FUI, uses reconstructed fishing effort data to estimate fuel use based on vessel size and fishing times. Both methods utilize assumptions which are inherently uncertain; the advantages and disadvantages of each method are discussed. The two approaches are found to be complementary to one another, not contradictory, and global estimates of CO 2 emissions from marine fishing should be based on a combination of both approaches, depending on the data locally available.