As the world is facing crisis due to the dwindling resources of fossil fuels, rapid depletion of conventional energy is a matter of serious concern for the mankind. So there is a necessity to find alternate fuels. Vegetable oils, because of their agricultural origin, due to less carbon content compared to mineral diesel are producing less CO₂ emissions to the atmosphere is used as an alternate fuel in substitute to diesel fuel. In the present study optimum compression ratio for VCR diesel engine fuelled with Jatropha oil blends with diesel (30%) has been determined at 203 bars injector opening pressure, 23⁰ CA BTDC injection timing and at 1500 rev/min rated speed. The test results revealed that compression ratio 19 exhibited better performance and lower emissions and hence, is considered as optimum compression ratio.