Delivering reductions in greenhouse gas emissions from the aviation sector requires support and action from all tiers of government. There has been considerable focus on the policies that can be implemented at international and national levels; however, sub-national bodies can also play an important and influential role. In order to identify what this role may be, it is important for sub-national governments to have an understanding of the size of their potential emissions responsibility. At present there is no widely accepted methodology for the apportionment of either international or domestic aviation emissions to sub-national levels. This paper assesses a number of existing consumer- and producer-based CO2 apportionment regimes that could be used to allocate the emissions from aviation to regional and other sub-national levels. This is followed by the presentation of a new hybrid consumer–producer apportionment regime applicable to aviation. This new approach is designed to provide an emissions baseline for a region that reflects its share of responsibility for the UK’s aviation emissions as both a producer of emissions and consumer of the services provided by aviation.