An analytical procedure is described for the determination of dissolved oxygen and methane in groundwater samples. The method consists of generating a helium gas headspace in a water filled bottle, and analysis of the headspace by gas chromatography. Other permanent gases such as nitrogen, and volatile aliphatic hydrocarbons such as ethane, propane, and butane could also be analyzed. BTX analyses could also be done on the sample. Detection limit for oxygen was 0.1 mg/1 and 0.002 mg/1 for methane. Good agreement was shown between Winkler titration and the GC-Headspace Equilibration Technique for oxygen analyses by a linear regression coefficient, R(sup 2)=0.998. Oxygen was greatly depleted in some field samples when they were stored for 30 days at 4 C without hydrochloric acid preservation. (Copyright (c) 1989 Gordon and Breach, Science Publishers, Inc.)