After World War II, with its advent of nuclear energy, one of the peaceful uses of nuclear energy was the development of neutron activation analysis (NAA) as an accurate tool for characterizations of elements in a variety of matrices. NAA is a technique based on irradiation in a nuclear reactor or other irradiation source and measuring resultant radioactivity of specific isotopes; it is a very accurate and precise technique. A large body of data exists on the applications of this technique to crude oil and petroleum products. At one time, several universities in the United States, such as the University of Kentucky, University of California at San Diego, University of California at Irvine, Purdue University, University of Missouri, Georgia Tech, Texas A&M University, Cornell University, University of Oregon, University of Maryland, and Washington State University, had active programs in NAA of fossil fuels and other matrices. Because of the difficulty of access to a nuclear reactor and associated radiation hazards, however, it has found only limited use in petrochemical or oil company laboratories. But one does not need one's own nuclear reactor for NAA because several commercial companies provide such services at a reasonable price. The universities mentioned also provide irradiation services to interested parties.