The present study is dedicated to the reforming of diesel fuel with diesel engine exhaust gas (i.e., air, CO₂, and H₂O mixture) using a nonthermal plasma torch for a NO_x trap regeneration application. The plasma technology developed is based on a high voltage/low current nonthermal plasma torch. In the first part of the paper, experimental results on synthesis gas production from exhaust gas fuel reforming of diesel fuel are reported. In the second part of the paper, these experimental results are compared with a 1D multistage model using n-heptane as a surrogate molecule for diesel fuel. Two compositions of synthetic diesel engine exhaust gas, corresponding to high and low engine loads, have been studied. It has been demonstrated that the oxygen from CO₂ and H₂O hardly ever intervenes in the reforming reactions. In the most favorable condition corresponding to a higher O₂ rate, a production of 7 × 10⁻³ mol·s⁻¹ of syngas has been reached, corresponding to an energy efficiency and a conversion rate of 40% and 95%, respectively. The 1D multistage model shows fair trends with experimental results despite an important shift mainly due to thermal losses, which are not taken into account in the 1D model. From these results and considering a real NO_x trap regeneration onboard application, it can be estimated for the most favorable case that, during the regeneration phase (approximately 12 s every 11 km), the power needed to run the plasma will be around 2.2% of the engine power.