The quantity of gasoline and middle distillate fuels in transit and storage makes these fuels the most common hydrocarbon contaminants in groundwater. Groundwater cart be contaminated by hydrocarbons from surface spills, transportation accidents, leaking above ground storage ranks, leaking underground service station tanks, and leaking interstate pipelines. Groundwater flows can be tracked by many methods, but fluorescence detection of dyes is both simple and easy. Fluorescein is a dye that has been successfully used for tracing groundwater flow. This dye is easily detectable at the 10(-11) M concentration and is relatively nontoxic. Results from this study showed that gasoline-contaminated water does not reduce the fluorescence intensity of fluorescein, but that a like amount of middle distillate does diminish the fluorescence intensity of fluorescein.