A promoted iron Fischer-Tropsch synthesis catalyst is used in a slurry reactor to evaluate and compare the selectivity and yields of total hydrocarbons, light alkenes (C-2-C-3) and intermediate range (C-6-C-16) linear-alpha-alkenes for syngas derived from natural gas and coal. The catalyst has a high hydrocarbon yield of 0.6 g (of hydrocarbon)/h-g Fe at high CO conversions (>85%). The syngas derived from coal produces a slightly higher total hydrocarbon yield than natural gas-derived syngas, due to a lower reactor partial pressure of water which inhibits the Fischer-Tropsch reaction rate. The natural gas-derived syngas produces a lighter and more paraffinic hydrocarbon product than coal-derived syngas. The selectivity and yields of light alkenes as well as the intermediate range linear-alpha-alkenes decrease considerably with reaction time and CO conversion for syngas derived from both sources. The yields of these valuable products can be considerably improved by a lower single-pass reactor CO conversion with recycle of unconverted syngas or by using reactors in series. The syngas derived from coal produces a slightly lower ethylene and propylene yield, but a higher intermediate-range linear-alpha-alkene yield than that of natural gas-derived syngas.