The need for fossil fuels is increasing every year. Various threats were made to obtain efficient fuel consumption. This study aims to determine the effect of Pertamina Dex and biodiesel on RPM and fuel consumption. The method used is an experiment on a diesel engine. Mixing Pertamina Dex fuel and biodiesel with a certain composition. The mixing variations were 0%, 10%, 30%, 40%, and 50% biodiesel and variations at 1000RPM, 1500RPM, and 2000RPM. The results of this study are (1) Pertamina Dex 100% is the most efficient fuel at 1000 RPM and 1500 RPM, (2) a mixture of 70% Pertamina Dex 30% Biodiesel is the most efficient fuel at 2000 RPM, and (3) Pertamina Dex 100% is the most fuel-efficient at 1000, 2000 and 3000 RPM.