Two methods for determining fuel contamination in groundwaters are compared. The first is based on headspace extraction, while the other utilizes purge and frap. Analyses, in both cases, are made by gas chromotography/flame ionization detection, with benzene, toluene, and xylene isomers as monitoring agents for fuel leaks. When compared, results show satisfactory agreement if we take into account the high levels of fuel contamination found in samples collected in control wells from a gas station in an urban site. Thus headspace/gas chromatography can be used, as an alternative technique, to monitoring of volatile organic compounds in groundwater. The main advantages when compared to purge and trap/gas chromatography are simplicity low cost, and automatic sample handling. When a mass spectrometry detector was used, ethylmethylbenzene and trimethylbenzene isomers were detected in the water samples. These compounds could also be used as alternative tracers for fuel leak defection.