Staying within the 2 ° C temperature increase target for climate change requires for ambitious emission reduction targets for the 2012–2020 compliance period. Cost-efficiency is a crucial criterion for the achievement of such targets, requiring analyses of all possible options. Enhancing the oceanic carbon sink via oceanironfertilization (OIF) provides such an option. Our analysis reveals that the critical unit costs per net ton of CO2 sequestered by OIF range from 22 to 28 USD (price level 2000) in a post-Kyoto compliance scenario. The critical unit costs are defined as those that would make an emitter indifferent between various abatement options. With reference to hypothetical short-term large-scale Southern Ocean OIF we are able to show that seven years of OIF provide a number of credits exceeding those obtainable from global forestation projects lasting 20 years. From an economic perspective, our results indicate that OIF can be considered a potentially viable carbon-removal option. However, further research is needed, especially on adverse side-effects and their ecological and economical consequences.