Polynuclear aromatic hydrocarbon (PAH) concentrations in nearshore coastal sediments offshore of Matagorda, TX, average 29 ± 28 (SD) ppb compared to 96 ± 112 ppb for the sediments in adjacent coastal estuaries and bays. PAHs were analyzed in bottom sediments collected in the vicinity of a multiwell platform in ~25 m of water, where six wells had been drilled between May 1982 and November 1985. The most elevated PAH concentrations were restricted to within 25 m of the platform discharge point. Mean PAH concentrations for two samplings at 10 and 25 m from the platform were 494 ± 251 and 757 ± 1820 ppb, respectively. The contaminated platform sites (≤25 m distant) were dominated by two-ring aromatics while the estuarine/bay and noncontaminated coastal sites were dominated by four- and five-ring aromatic hydrocarbons. Phenanthrene/anthracene ratios suggest a petroleum source for the hydrocarbons at platform stations and pyrolytic sources for the bay/estuarine hydrocarbons. © 1990, American Chemical Society. All rights reserved.