The combination of high crude oil prices, energy security concerns and environmental drivers have resulted in an increased focus on alternative fuels. Gas to liquids (GTL) diesel is considered to be a promising alternative diesel fuel, given that it can be used directly as a diesel fuel or be blended with petroleum-derived diesel or biodiesel. GTL diesel fuels are predominantly paraffinic and possess several excellent inherent properties including virtually zero sulfur, very low aromatics (≺1%) and very high cetane values (typically ≻75).Currently GTL diesel is mostly sold into the European market as a blend stock for the extending and upgrading of petroleum-derived diesel fuels. Given GTL diesel's inherent paraffinic nature, the density of this product is below the European minimum 820 kg/m₃ EN590 specification (at 15°C). Typically up to 20% (vol) GTL diesel can be blended into crude-oil-derived diesel in order to meet the minimum European density specification, although neat applications of GTL diesel have also received some attention in literature. This study presents some findings pertaining to injector fouling for neat and 20% (vol) GTL diesel blends on a variety of diesel engines. There is however, very little information in the open literature on the physical and injector fouling performance properties of higher binary blends of petroleum-derived and GTL diesel. Several markets do not have a minimum density specification (e.g., the USA, Canada, Uzbekistan), while several countries have winter density specifications lower than 820 kg/m₃, including countries like China, potentially enabling GTL diesel to be used at higher blending ratios and in its neat form.In the current study, neat low temperature Fischer Tropsch (LTFT) GTL diesel and EN590 diesel fuels, together with blends containing 10, 20, 30, 50, and 80 volume percent GTL, were analyzed for their physical and chemical properties. The injector fouling performances of these blends were assessed in the CEC F-23-01 XUD9 and Sasol common rail tests. Many of the physical properties of these blends were influenced positively by the addition of GTL diesel to the EN590 fuel. Overall, it was concluded that at low percentages, blends of GTL diesel with EN590 resulted in similar injector fouling performance in the CEC F-23-01 XUD9 and Sasol common rail tests. At higher GTL diesel contents, a significant injector fouling performance improvement was found.