Samples of water and bivalve mollusks were collected during the 2-day period immediately following a spill of gasoline in Block Island Sound, RI, and were analyzed by gas chromatography and gas chromatography-mass spectrometry. These analyses showed gasoline compounds in the water column at concentrations up to 20 micrograms/L even though a visible slick was not present. Additionally, very low levels of hydrocarbons, which might have originated from the gasoline spill, were detected in bivalves from the area. The analytical protocol used for examining these water samples was carefully evaluated for its expediency and accuracy in detecting gasoline compounds in a field sampling situation. The method proved to be rapid, introduced only minimal levels of contamination, and consistently returned 60% of the gasoline compounds. Although it is difficult to quantitatively handle volatile organic compounds in a field sampling situation, this study indicated that a marine gasoline spill could be quickly and efficiently monitored by using the described methods.