In order to determine the origin of polycyclic aromatic hydrocarbons (PAHs) in sediments from Narragansett Bay, Rhode Island, the PAH assemblages from the sediments and from possible origin materials were analyzed by gas chromatographic and gas chromatographic-mass spectrometric techniques. Analyses included determinations of: (1) the relative content of non-alkylated PAH parent molecules, i.e. parent compound distributions (PCDs); (2) alkylation patterns of these PAH molecules, i.e. alkyl homolog distributions (AHDs); and (3) phenanthrene/anthracene (P/A) ratios. Samples from the Narragansett Bay transect, which began at a sewage outfall for the City of East Providence, Rhode Island, and ended 20km to the south, showed rapidly decreasing concentrations of PAH compounds with increasing distance from Providence. The PAH assemblages in transect sediments surrounding tarred piers were contaminated by coal tar used to coat the pilings. The close resemblance of PCDs from bay sediments and combustion products indicated that the PAHs in the transect sediments were predominantly combustion generated. While evidence for the input of PAHs from petroleum to bay sediments appeared in some AHDs of upper bay transect sediments, AHDs from the lower (less polluted) end of the transect showed less influence of petroleum PAH contamination. In general, the shapes of AHDs from transect sediments of Narragansett Bay appeared to be best explained by a combination of inputs of PAHs from petroleum and combustion processes, rather than by the solubility alteration of PAH assemblages on incoming airborne material.