The present study attempts to compare two recently proposed concepts for the direct removal of carbon dioxide from the emissions of large hydrocarbon-fueled power plants. The more specific case of an existing 500 MW natural gas plant is examined. At first, previously published calculations corresponding to the pre-combustion scheme of Mori et al. (1991), based on methane reforming, are summarized. Flue gas treatment, coupled with air separation upstream of the boiler, as proposed by Golomb et al. (1989), is then applied to the same existing 500 MW plant. In this fashion, the two methods can be consistently compared. Pre-combustion fuel processing appears to result in lower power cost penalties, of the order of 30%, whereas the post-flame separation technology considered here would impose a power cost increase of nearly 50%.