Spark ignition engines are very popular engines that they are running millions of vehicles all over the world. This engine emits many harmful pollutants, such as CO, UHC, and NOX. In this paper, the impact of gasoline octane number on the engine performance and exhaust emissions was studied. In the tests, four-cylinder, four-stroke engine, and two variable octane numbers (RON83 and 94.5) were used. The engine was run at different engine speeds and loads. The results from the experimental study indicated that the brake specific fuel consumption (bsfc) of RON94.5 was higher than RON83 by 13.93%, while the brake thermal efficiency (ƞbth) was higher for RON83 compared to RON94.5 by 12.31%. The emitted emissions for the tested fuels were high when RON83 was used compared to RON94.5 by 65.52%, 49.11%, and 57.33% for CO, UHC, and NOX, respectively.