The need to improve the performance characteristics of the gasoline engine has necessitated the present research. Increasing the compression ratio below detonating values to improve on the performance is an option. The compression ratio is a factor that influences the performance characteristics of internal combustion engines. This work is an experimental and theoretical investigation of the influence of the compression ratio on the brake power, brake thermal efficiency, brake mean effective pressure and specific fuel consumption of the Ricardo variable compression ratio spark ignition engine. Compression ratios of 5, 6, 7, 8 and 9, and engine speeds of 1100 to 1600 rpm, in increments of 100 rpm, were utilised. The results show that as the compression ratio increases, the actual fuel consumption decreases averagely by 7.75%, brake thermal efficiency improves by 8.49 % and brake power also improves by 1.34%. The maximum compression ratio corresponding to maximum brake power, brake thermal efficiency, brake mean effective pressure and lowest specific fuel consumption is 9.The theoretical values were compared with experimental values. The grand averages of the percentage errors between the theoretical and experimental values for all the parameters were evaluated. The small values of the percentage errors between the theoretical and experimental values show that there is agreement between the theoretical and experimental performance characteristics of the engine.