In general, offsetting is done through the purchase and cancellation of emissions units, arising from different sources of emissions reductions achieved through mechanisms (e.g. UNFCCC’s Clean Development Mechanism), programmes (e.g. REDD+) or projects (e.g. substituting coal-fired stoves with solar cookers).

The buying and selling of eligible emissions units happens through carbon market. The price of the emissions units in the carbon market is influenced by the law of supply (availability of emissions units) and demand (level of offsetting requirements).

For CORSIA, an aeroplane operator is required to meet its offsetting requirements by cancelling CORSIA Eligible Emissions Units in a quantity equal to its total final offsetting requirements for a given compliance period. CORSIA Eligible Emissions Units are to be determined by the ICAO Council, and information on eligible units will be made available on the ICAO CORSIA website.