This discussion paper estimates the potential supply of certified emission reductions (CERs) from projects registered under the Clean Development Mechanism (CDM) for the period 2013 to 2020. The supply potential estimation considers the most recent information on the status of CDM projects and their ability to issue CERs, if sufficient demand were recreated on short-term. The actual current demand for CERs is still low but could increase if CERs were used beyond the Kyoto Protocol (for example under CORSIA). When considering options for using CERs from registered projects, a key question for policy makers is whether the projects are likely to continue greenhouse gas (GHG) abatement even in the absence of CDM revenues or whether they are vulnerable of discontinuing abatement. Drawing upon recent research, this paper differentiates the CER supply potential between projects that are vulnerable of discontinuing GHG abatement and those that are not. The CER supply potential is estimated based on a bottom-up model that reflects recent research on the status and operation of CDM project activities as well as regulatory requirements of the CDM which could limit the ability to issue CERs, with the view to providing a realistic estimate of the CER supply potential.