New diesel-type fuels such as biodiesels and gas-to-liquid (GTL) fuel have been developed in order to aid vehicle manufacturers in achieving forthcoming emission regulations, by improving engine out emissions and exhaust gas after-treatment performance. Furthermore, synthetic fuels are virtually free of sulfur and aromatic hydrocarbons and can improve the performance and durability of the catalytic fuel reformers that are designed to provide H-2 to fuel cells, internal combustion (IC) engines, and after-treatments. Combustion and exhaust-gas reforming experiments with GTL and ultralow sulfur diesel (ULSD) were run under several engine and reformer operating regimes. Using a single cylinder bench engine, the combustion of GTL fuel (and blends with conventional diesel fuel) was found to reduce NOx emissions substantially and improve engine thermal efficiency but led to an increase in smoke for the default injection timing in the experiment. However, by optimizing the injection timing in a GTL-fueled engine, the harmful emissions of NOx and smoke were both reduced simultaneously while still giving improvements in engine thermal efficiency. In general, it was found that the NOx/particulates tradeoff curve shifted to lower emissions for GTL fuel and GTL fuel blends. During exhaust-gas reforming, the use of GTL fuel was found to increase fuel conversion, while producing more hydrogen and less methane.