Co-firing offers a near-term solution for reducing CO(2) emissions from conventional fossil fuel power plants. Viable alternatives to long-term CO(2) reduction technologies such as CO(2) sequestration, oxy-firing and carbon loop combustion are being discussed, but all of them remain in the early to mid stages of development Co-firing, on the other hand, is a well-proven technology and is in regular use though does not eliminate CO(2) emissions entirely. An incremental gain in CO(2) reduction can be achieved by immediate implementation of biomass co-firing in nearly all coal-fired power plants with minimum modifications and moderate investment, making co-firing a near-term solution for the greenhouse gas emission problem. If a majority of coal-fired boilers operating around the world adopt co-firing systems, the total reduction in CO(2) emissions would be substantial. It is the most efficient means of power generation from biomass, and it thus offers CO(2) avoidance cost lower than that for CO(2) sequestration from existing power plants. The present analysis examines several co-firing options including a novel option external (indirect) firing using combustion or gasification in an existing coal or oil fired plant Capital and operating costs of such external units are calculated to determine the return on investment. Two of these indirect co-firing options are analyzed along with the option of direct co-firing of biomass in pulverizing mills to compare their operational merits and cost advantages with the gasification option. (c) 2010 Elsevier Ltd. All rights reserved.