An improved method for molecular and stable isotope analysis of gasoline range hydrocarbons (C 5 -C 1 0 ) in oils uses Solid Phase Microextraction. Analytes are sampled from the headspace above oil droplets and analyzed by gas chromatography and continuous-flow isotope-ratio mass spectrometry. Analytical considerations with this sampling technique include equilibration times, vapor pressure/temperature effects, and the presence of a complex matrix. Instrumentation factors such as column/split flows are also considered. The results are compared with an alternative purge and trap method. Molecular analyses prove reproducible between the two methods, however, stable carbon isotope ratios exhibit a non-systematic depletion and enrichment of 0.2-2.0%% for 16 pre-selected compounds.