Abstract: Distributing units of carbon emission reduction (“CER”) comprises obtaining a right to purchase CERs in the future that are developed by emission reduction projects, dividing the future CERs into a plurality of tranches, committing the future CERs in the tranches to prospective buyers, and distributing CERs received from the projects to the prospective buyers based on a priority of delivery between the tranches. A contingent call option can provide replacement CERs to meet CER obligations to a senior tranche if received CERs are not sufficient to meet the obligations of future CERs allocated to buyers in the senior tranche. CERs are not distributed to buyers of junior tranches if the received CERs are not sufficient to meet the CER obligations to more senior tranches.