In considering how the International Civil Aviation Organization (ICAO) might construct a global market based measure to assist airlines in meeting international civil aviation’s goal of capping carbon dioxide emissions at 2020 levels, the authors review different perspectives on one element of the design of the market based measure. Specifically, insofar as achieving “carbon neutral growth from 2020” entails not only reducing international aviation’s emissions as much as possible, but also procuring, via carbon markets, emission reductions to offset emissions above 2020 levels, then a key question becomes how offset responsibilities will be distributed between and among participating airlines. Bridging differences between States on the issue of allocation of offset responsibilities is crucial to the adoption of an ICAO market based measure. After reviewing briefly the historical context for the allocation debate, namely CBDR and its counterpart concept in ICAO, the concept of special circumstances and respective capabilities, the authors propose that States address distribution of offset obligations in ICAO by starting with the 100% sectoral approach, with an important modification: any carrier that reduces its individual emissions below a three-year average baseline may “keep” or save its reductions as a credit against its offset obligations. Such an approach could encourage carriers to invest in in-sector reductions, help them reap the benefit of those investments, generate cost-savings, and bridge differences over the distribution of offset obligations in a way that provides equal and fair opportunities to all carriers.