The performance, emissions and combustion characteristics of a spark ignition engine at varying compression ratio and spark timing using two grades of gasoline in Saudi Arabian market, RON91 and RON95 have been presented on this paper. The tests were conducted using a single cylinder, four-stroke spark ignition research engine that operates with different RON fuel. The experiments were conducted at a wide-open throttle with an engine speed of 2500 rpm at stoichiometric conditions for three different compression ratios (9.5:1, 10:1, 10.5:1). At each compression ratio, the spark timing was varied till knocking is detected. The performance characteristics such as brake power, specific fuel consumption, thermal efficiency, in-cylinder pressure, rate of heat release, and exhaust emissions were analyzed. The data shows that the increasing of compression ratio and spark timing increased the brake power and decreased the brake fuel consumption for both type of fuels. Increasing compression ratio was more advantageous for RON95 due to the auto-ignition resistance event. The NO_x emission was insignificantly decreasing as compression ratio increases with lower NO_x emission from RON91. Compression ratio had considerable effect on CO emission for both fuels.