A study was performed to quantify the impact of blending Fatty Acid Methyl Ester (FAME) with Gas-to-Liquids (GTL) diesel fuel on engine exhaust emissions. Fuels that were considered in the study included blends of GTL and EN590 diesel containing 0, 7, and 20 volume % of Soy and Rapeseed Methyl Ester (SME and RME). Part of the study focused on European engine technology, and tests were performed on a Euro 3 passenger car engine and a Euro V heavy-duty engine. A limited study was performed using a heavy-duty engine meeting the US 2004 emission standards, in which case comparisons between the GTL diesel and FAME blends were made with US 2D and California Air Resources Board (CARB) reference fuels.The results showed particulate mass (PM) reductions to varying degrees with all of the GTL/FAME blends. The European heavy-duty engine showed a nominally neutral nitrogen oxides (NOx) emission response with the addition of FAME to either the EN590 or GTL diesel fuels, while an increase in NOx emissions was found with the US heavy-duty engine. Nonetheless, a 20% blend of SME with GTL diesel matched the NOx emissions of the CARB reference diesel fuel. The results show that, in general, the favorable exhaust emission properties of GTL diesel, specifically in terms of NOx and PM reductions, are maintained when FAME is added.