The methanol has greater resistance to knock and it emits lower emissions than neat gasoline. As single cylinder small engines have low compression ratio (CR), and they run with slightly rich mixture, their power are low and emission values are high. The performance can be increased at high CR if these engines are run with fuels which have high octane number. In this study, methanol was used at high CR to increase performance and decrease emissions of a single-cylinder engine. Initially, the engine whose CR was 6/1 was tested with gasoline and methanol at full load and various speeds. Then, the CR was raised from 6/1 to 8/1 and 10/1, gradually. The knock was not observed at the CRs of 8/1 and 10/1 when using methanol while the knock was observed at the CR of 8/1 when using gasoline. The knock was determined from the cylinder pressure-time curves. The results showed that some decreases were obtained in CO, CO2 and NOx emissions without any noticeable power loss when using methanol at the CR of 6/1. By increasing the CR from 6/1 to 10/1 with methanol, the engine power and brake thermal efficiency increased by up to 14% and 36%, respectively. Moreover, CO, CO2 and NOx emissions were reduced by about 37%, 30% and 22%, respectively. (C) 2010 Elsevier Ltd. All rights reserved.