Bioremediation is a process that uses naturally occurring or genetically engineered microorganisms such as yeast, fungi, and bacteria to transform harmful substances into less toxic or nontoxic substances. The objective of bioremediation is to stimulate the growth of indigenous or introduced microorganisms in regions of subsurface contamination and, thus, provide direct contact between microorganisms and the dissolved and sorbed contaminants for biotransformation. The advantage of bioremediation is that it is a natural process, it destroys target chemicals at the contamination site, and the process is usually less expensive than other methods used for cleanup of hazardous wastes. Bioremediation has been used since the late 1970s to degrade petroleum products and hydrocarbons. A few species of bacteria, such as some members of the genus pseudomonas, can use crude oil for energy. Bioremediation action, such as spraying the area with nutrients to enhance the growth of native microorganisms, has worked beautifully.