We calculated carbon and energy flows in 11 models of FT plants. While uncertainties are substantial, our best- guess estimates indicate that FT diesel is economically competitive, with fuel costs comparable to fossil diesel derived from oil at 34 $/bbl for GTL, 60 $/bbl for CTL and 75 or more $/bbl for BTL. GHG emissions are substantially higher for CTL, about equal to fossil diesel for GTL and possible (much) lower for BTL. Important uncertainties, to order of tens of percents, were found in the data for component costs, variability in prices of feedstocks and co- products, and the GHG impact of producing biomass.