This report has been produced for the Working Group on Sustainable Mobility under the Nordic Council of Ministers. The report includes a review and assessment of the data and methodologies in relation to calculation and reporting of the energy consumption and greenhouse gas emissions from international aviation, as well as issues related to allocation of these emissions to countries. The emphasis is on the assessment of opportunities, advantages and disadvantages of the different methodologies and principles for allocation to the Nordic countries. CO2 emissions from international aviation are not covered by the reduction and limitation commitments under the Kyoto Protocol. However, the emissions from international aviation are growing rapidly, and if they are to be included in the reduction efforts by Annex I countries, they will have to be allocated to parties who are or will become responsible in relation to the reduction commitments of the Protocol. The Nordic governments have expressed concern about the increase of international greenhouse gas emissions from international aviation, and are therefore interested in an analysis and assessment of the options for quantifying and allocating the emissions from international aviation to the Nordic countries.