GTL (Gas-To-Liquid) fuel is well known to improve tailpipe emissions when fuelling a conventional diesel vehicle, that is, one optimized to conventional fuel. This investigation assesses the additional potential for GTL fuel in a GTL-dedicated vehicle.This potential for GTL fuel was quantified in an EU 4 6-cylinder serial production engine. In the first stage, a comparison of engine performance was made of GTL fuel against conventional diesel, using identical engine calibrations. Next, adaptations enabled the full potential of GTL fuel within a dedicated calibration to be assessed. For this stage, two optimization goals were investigated: - Minimization of NOx emissions and - Minimization of fuel consumption.For each optimization the boundary condition was that emissions should be within the EU5 level. An additional constraint on the latter strategy required noise levels to remain within the baseline reference.Optimizing the calibration for GTL fuel led to further substantial reductions of regulated emissions, i.e., achieving EU 5 levels with a former EU 4 vehicle, as well as significantly reduced exhaust CO₂ emissions.The use of GTL fuel in combination with a dedicated calibration already achieves a significant benefit, even before consideration of potential hardware modifications. This would allow an improved emissions level for compliance with required local legislation.