Oxygenated compounds (alcohols and ethers) have attracted attention as additives to gasoline to improve fuel specifications. These have a high octane number and contain oxygen. So, they decrease the knocking tendency and lead to the lowering of some exhaust emissions such as carbon monoxide (CO). In this study, methyl tertiary butyl ether (MTBE), a well-known oxygenate, was considered as a gasoline additive. The effects of MTBE-blended fuels with various blending rates (0, 5, 10, 20, and 30 vol.%) on engine performance and exhaust emissions were investigated using a Ricardo/Hydra, single cylinder, four-stroke spark ignition, fuel injection engine. The experiments were performed at engine speeds of 1500-5000 rpm with increments of 500 rpm at full load and a compression ratio of 10:1. The result of the engine tests indicated that engine torque was similar or close to unleaded gasoline (MTBE0) at MTBE percentages up to 10%. Moreover, MTBE blends improved brake thermal efficiency and decreased brake specific energy consumption. Regarding exhaust emissions, CO and HC emissions reduced with the increase of MTBE content in the blended fuel, but HC emissions did not decrease as much as CO emissions did. Furthermore, the concentration of NO increased for MTBE blends owing to oxygen enrichment. (C) 2015 Elsevier B.V. All rights reserved.