Methyl tert-butyl ether (MTBE) is added to gasoline to enhance the octane number of gasoline, tert-butyl alcohol (TBA) is major degradation intermediate of MTBE in environment, and benzene, toluene, ethyl benzene and xylene (BTEX) are also major constituents of gasoline. In this study, a simplified headspace analysis method was adapted for simultaneous determination of MTBE, TBA and BTEX in ground water samples. The sample 5.0 mL and 2 g NaCl were placed in a 10 mL vial and the solution was spiked with fluorobenzene as an internal standard and sealed with a cap. The vial was placed in a heating block at 85 $^{circ}C$ for 30 min. The detection limits of the assay were 0.01 ${mu}$g/L for MTBE and BTEX, and 0.02 ${mu}$g/L for TBA. The method was used to analyze 110 ground water samples from various regions in Korea, and to survey the their background concentration in ground water in Korea. The samples revealed MTBE concentrations in the range of 0.01 - 0.45 ${mu}$g/L (detection frequency of 57.3%), TBA concentrations in the range of 0.02 - 0.08 ${mu}$g/L (detection frequency of 5.5%), and total BTEX concentrations in the range of 0.01 - 2.09 ${mu}$g/L (detection frequency of 87.3%). The developed method may be used when simultaneously determining the amount of MTBE, TBA and BTEX in water.