This book discuss about performance and exhaust emissions of spark ignition engines using conventional fuels and alternative fuels. The emissions from conventional fuel vehicles have adverse effect on human body and playing an important role in formation of the greenhouse effect, acid rain and global warming. These issues can be mitigated to a great extant by using alternative fuels such as natural gas, liquefied petroleum gas (LPG), and their mixture. Use of alternative fuels greatly reduces the hydrocarbon and carbon monoxide emissions. Hydrocarbon emissions for gasoline, LPG and mixture fuels recorded 69, 19 and 24 ppm respectively. CO emissions for LPG, gasoline and mixture fuel engines are 0.85, 5.2 and 2.7 % respectively. LPG fuel engine is more economical but in most of the cases it results in about 10 -15% power loss in comparison to gasoline fuel engine.