This report proposes an ancillary services payment mechanism for the Chilean electricity supply industry. This is accomplished in three steps. The first section presents a set of economic principles for assessing the likely performance of candidate ancillary services payment mechanisms in the context of Chilean electricity supply industry. The second section uses this framework to assess the likely performance of the ancillary services payment mechanism recently proposed by the National Energy Commission (NEC) in its letter Number 715 dated September 21, 2010. The third section formulates an alternative payment mechanism that respects the existing electricity market structures and rules in Chile, but is likely to provide lower cost and more reliable solution than the one proposed by the NEC. An appendix outlines several examples of how the proposed procurement mechanism could be implemented and how potential exercise of market power by a dominant supplier of any ancillary service could be mitigated.