An atmospheric-pressure, mlcrowave-lnduced, helium plasma system for oxygen-selective gas chromatographic detection of petroleum-related samples Is presented. Extensive purification of the helium plasma gas, exclusion of atmospheric oxygen, and use of an appropriate plasma containment tube were crucial to minimize oxygen spectral emission produced by Impurities In the plasma gas, air leaks, back diffusion of air Into the plasma, and the plasma'containment tube Itself. With these precautions, the oxygen-to-carbon selectivity Is 103. This Is the best oxygen selectivity reported In the literature to date for a mlcrowave-lnduced plasma detector system. The system Is sensitive down to 2 ppmw (parts per million by weight) oxygen for narrow-boiling range distillates and simple mixtures and 500 ppmw oxygen for wide-boiling range, complex samples. The detector Is linear over 3 orders of magnitude and has a uniform response to different types of oxygenates. Examples Illustrate the feasibility of gas chromatography/mlcrowave-lnduced plasma for detecting organic oxygenated compounds in simple mixtures and In petroleum and synfuel distillates boiling up to ca. 500 °F.