The development of coal mine methane (CMM) projects is subject to various kinds of risk, one of these being their highly variable methane content. In this study, a new methodology is proposed to reflect the impact of this uncertainty on a negotiated Certified Emission Reduction (CER) price, which is based on the available information. To simulate a process of price negotiation the Rubinstein-Ståhl bargaining game is utilized, where a buyer’s discount factor is unknown. It is assumed that a buyer’s willingness to accomplish price negotiations depends on the CER uncertainty. The bargaining model has been extended by introducing dependence of its three parameters on the probability of a failure to fulfil the contracted CER amount.