A review. The fuel oxygenate Me tert-Bu ether (MTBE) is one of the most frequently detected volatile org. compds. in groundwater and, thus, has become a priority groundwater pollutant over the last decade. Methods for the quant. detn. and for compd.-specific isotope anal. (CSIA) of MTBE and its key degrdn. intermediate, tert-Bu alc. (TBA), in ground- and surface water are reviewed. These compds. are exclusively analyzed by gas chromatog. (GC), mainly with mass spectrometric (MS) detection because of the requirements for selectivity and sensitivity. Sample introduction/enrichment based on direct aq. injection, headspace anal., solid-phase microextn. (direct immersion and headspace), and purge-and-trap is discussed. Specific advantages and disadvantages of these techniques are compared and criteria are given for choosing an appropriate method. Furthermore, it is shown that CSIA can be used to det. the isotopic compn. of MTBE and related compds. in the low mg/L range and will therefore become an invaluable tool in the characterization of the environmental fate of such pollutants.