Oil discharges and spills from industrial plants and ships impart unpleasant tastes and odor to water and to game fish and fowl, as well as affect the amenities of beach and recreational facilities. For enforcement actions, it has been useful not only to identify the source of oil spills in the streams, but also to characterize first the petroleum product involved. Methods developed in the last two years at the Analytical Quality Control Laboratory are described; the author presents a workable scheme for the characterization and identification of residual oil pollutants found in surface waters. A powerful aid for the characterization of fuel oil products is stressed. Identity with gas chromatographic and infrared data is given in an elaborate fashion and comparisons are made in the absence of extremely expensive analytical equipment.