Methyl tertiary - butyl ether (MTBE) is the most common fuel oxygenate and octane booster currently used in unleaded gasoline in Tehran. It can be easily and cheaply produced at the refinery. Mixing of 5-15 percent of this compound can make a significant decrease in reduction of air pollutant such as CO, NOx, … . Besides the above advantages, the water solubility of MTBE is so high, therefore it has high mobility downward in soil because it dose not readily adsorb or attach on soil. It is readily soluble in water it can reach ground water quickly and easily.The main contributors of gasoline containing MTBE into the subsurface environment of soil are underground storage tanks (UST), pipelines and refueling facilities.The drinking water sources Polluted by an undesirable taste and odors when its concentration ranges between 20-40 ppb. In this case high clean up costs is needed for remediation. In this project MTBE was detected in soil and water sources around gasoline pump stations in Tehran. All the samples were collected from wells near the pump stations, 2 samples from surface water and 2 samples from soil was accordance to determine the concentration of MTBE on surface.The analyzing method in this project purge & Trap / GC / MS Method, which was recommended by USEPA in 2001 for analyzing soil and water samples. The high detectable Concentration of MTBE belonged to samples, which were collected from wells next to huge storage tanks of Tehran refinery, and Rey installation.They were about 0.94 ppm and 0.34 ppm.There were no detectable MTBE in soil samples because after leakage it tends to migrate downward the soil.Laboratory duplicates and field duplicates were done for two samples to give a measure of the precision associated with laboratory procedures and sample collection and preserving. The concentrations of MTBE in two samples of surface water were 11 ppb and 6 ppb. The reason may be due to MTBE spills from repair shops or it is because of used motor oil which spills to the surface water.