Discussion paper: Marginal cost of CER supply and implications of demand sources estimates the marginal cost of supplying certified emissions reduction units (CERs) from projects that are currently registered under the Clean Development Mechanism (CDM). The paper developed a supply curve using data on the individual ability of projects to potentially supply CERs over the period up to 2020, and analyse changes to the supply curve based on a number of scenarios which restrict the eligibility of CERs based on the timing of emission reductions, the timing of project investment decisions and registration under the CDM, as well as an assessment of the extent to which projects are vulnerable to the risk of discontinuing abatement activities without CER revenues.