 This form of recovery is used extensively to increase oil extraction in the San Joaquin Valley, which yields a very heavy oil, yet accounts for ten percent of the United States' oil extraction.Fire flooding (In-situ burning) is another form of TEOR, but instead of steam, some of the oil is burned to heat the surrounding oil.Occasionally, surfactants (detergents) are injected to alter the surface tension between the water and the oil in the reservoir, mobilizing oil which would otherwise remain in the reservoir as residual oil.