The primary goal of this project has been to evaluate and compare the effect of the intrinsic differences between cobalt (Co) and iron (Fe) catalysts for Fischer-Tropsch (FT) synthesis using coal-derived syngas. Crude oil, especially heavy, high-sulfur crude, is no longer the appropriate source for the additional, or marginal, amounts of middle-distillate fuels needed to meet growing US and world demand for diesel and jet fuels. Only about 1/3 of the marginal crude oil barrel can be made into diesel and jet fuels. The remaining 2/3 contributes further to global surpluses of by-products. FT can produce these needed marginal, low-sulfur middle-distillate fuels more efficiently, with less environmental impact, and from abundant US domestic resources. Cobalt FT catalyst is more efficient, and less expensive overall, than iron FT catalyst. Mechanisms of cobalt FT catalyst functioning, and poisoning, have been elucidated. Each of these primary findings is amplified by several secondary findings, and these are presented, and verified in detail. The most effective step the United States can take to begin building toward improved long-term national energy security, and to reduce dependence, over time, on imported crude oil from unfriendly and increasingly unstable areas of the world, is to begin producing additional, or marginal amounts of, middle-distillate-type fuels, such as ultralow sulfur diesel (ULSD) and jet fuel (not gasoline) from US domestic resources other than petroleum. FT synthesis of these middle distillate fuels offers the advantage of being able to use abundant and affordable US coal and biomass as the primary feedstocks. Use of the cobalt FT catalyst system has been shown conclusively to be more effective and less expensive than the use of iron FT catalyst with syngas derived from coal, or from coal and biomass combined. This finding is demonstrated in detail for the initial case of a relatively small FT plant of about 2000 barrels per day based upon coal and biomass. The primary feature of such a plant, in the current situation in which no commercial FT plants are operating in the US, is that it requires a relatively modest capital investment, meaning that such a plant could actually be built, operated, and replicated in the near term. This is in contrast to the several-billion dollar investment, and accompanying risk, that would be required for a plant of more than an order of magnitude greater capacity, which has been referred to in the technical literature on fuel production as the capacity required to be considered "commercial-scale." The effects of more than ten different potential poisons for cobalt FT catalyst have been studied extensively and in detail using laboratory continuous-stirred tank reactors (CSTRs) and bottled laboratory syngas "spiked" with precisely controlled amounts of the poisons, typically at the levels of 10s or 100s of parts per billion. This data set has been generated and interpreted by world-renowned experts on FT catalysis at the University of Kentucky Center for Applied Energy Research (UK-CAER), and has enabled unprecedented insight regarding the many molecular-scale mechanisms that can play a role in the "poisoning" of cobalt FT catalyst.