Abstract: Oil contaminated ground water is purified by immersing one pump into the oil layer in the underground formation and another pump into the water layer in the underground formation and pumping the oil and water into, respectively, an oil storage tank and an oil/water separator. The water being pumped into the oil/water separator contains small amounts of emulsified oil which is separated from the water in the separator and forwarded to the oil storage tank. The water from the separator is passed through a series of filters to remove any trace amounts of oil present in the water so that the oil level in the purified water does not exceed 0.9 parts per billion.