A novel and simple method using solid phase microextraction (SPME) with poly(dimethylsiloxane) fiber coating and linear temperature-programmed retention index (LTPRI) has been developed to quantify petroleum hydrocarbons in water. Partition coefficients (K(fw)) for the analytes in water and SPME were established for a series of aromatics, cycloalkanes and alkanes. There is a linear relationship between log K(fw) for each hydrocarbon series and LTPRI. The slope of the curves for all the series are the same and related to the partial free energy of solution for the hydrocarbon-fiber coating solution. The y-intercept of the plots is distinct for each group of hydrocarbons and related to Henry's law coefficients for each series. Therefore, the K(fw) for a series of hydrocarbons can be estimated using literature Henry's law coefficients. This method was used to quantify BTEX-contaminated water.