Abstract: This paper studies the performance of single cylinder, 4-stroke, variable compression ratio, spark timing, and equivalence ratio, spark ignition Ricardo E6 engine, fuelled with supplemented hydrogen to LPG. The results indicated that the higher useful compression ratio (HUCR) for a mixture of two gasses was (10.5:1). The brake power when the engine was fueled with LPG had higher than that when it was fed with hydrogen. However, when mixing two fuels, the brake power increased and became greater than that when fueled with LPG to a certain limit (the hydrogen volumetric ratio in the mixture reached 70%). After this limit the brake power reduced by increasing hydrogen volumetric ratio. At equivalence ratios between (Ø=1-1.1), the brake power got its highest value when mixing the two fuels. The results showed that the engine could be operated with very lean equivalence ratios with additional hydrogen. The brake specific fuel consumption reduced while the indicated thermal efficiency increased when hydrogen volumetric fraction was increased.