<p>This study investigates eco-efficiency (EE) and its determinants in South Korean offshore fisheries from 2012 to 2020 to achieve carbon negativity in the fisheries sector. We applied a slack-based measure model with undesirable outputs and a random-effects Tobit model. The analysis revealed that the EE of offshore fisheries has been deteriorating over the years. An analysis of the determinants of EE showed that fleet fisheries operating with more than two fishing vessels or trawl fisheries towing fishing nets experienced a decrease in EE. Moreover, we found that as the vessel’s age increases, the EE of offshore fisheries diminishes. Finally, although the EE of offshore fisheries improves as the skipper’s age increases, it begins to decrease once they exceed 58&#xa0;years. Accordingly, the government should implement policies such as low-carbon gear replacement support through a carbon-neutral direct payment system, reduction in the scale of fleet fisheries, and financial support for fishermen participating in vessel modernization projects to improve the EE of offshore fisheries.</p>