The world's first large scale commercial Gas-to-Liquids (GTL) fuel production plant using low temperature Fischer-Tropsch (LTFT) technology, Oryx GTL, has been in operation in Qatar since 2007. The first on-specification diesel fuel produced by this plant was subjected to a comprehensive fit-for-purpose validation program, part of which comprised exhaust emission tests which were conducted with two different passenger cars and two different heavy-duty engines. Three neat GTL diesel fuels were included in the study: commercial GTL diesel fuel, an equivalent full boiling range GTL diesel fuel produced in a pilot plant, and a GTL diesel fuel with a narrower distillation range. Commercial sulfur-free (≺10 mg/kg) European EN590 diesel fuel was used as the reference fuel. In addition, tests were performed with two different blending ratios (20% and 50%) of GTL diesel in the EN590 diesel.The neat GTL fuels showed reductions in PM, THC, and CO, while NOx emissions were either neutral or reduced, depending on the engine technology, when compared to the EN590 diesel. The blended fuels generally showed reductions in emissions or a neutral response, in some cases with a distinct non-linear characteristic in relation to the blending ratio. The narrower cut of pilot plant GTL diesel fuel also showed a varied response relative to the full boiling range GTL diesel fuel, depending on the engine technology. The results of the tests demonstrated that the commercial GTL diesel fuel shows the same favorable exhaust emissions performance that has come to be expected from extensive testing conducted previously with GTL fuel produced in pilot plants. Interactions with engine technology, specifically in terms of fuel injection equipment, were also highlighted.