Optimization of the direct analysis of the sterol fraction of a sunflower oil is carried out by means of the modified sequential Simplex method. Sensitivity achievable with the on-line coupling of reversed phase liquid chromatography and gas capillary chromatography (RPLC−GC) using a programmed temperature vaporizer (PTV) as interface is enhanced by optimization of some experimental conditions, namely, transferred volume, purge flow rate during transfer, interface temperature, and time during which the gas purges the interface once the transfer is completed. The optimization procedure allows volume fractions higher than 3000 μL of water−methanol eluents to be transferred into the GC system, 2000 μL/min being the speed of sample introduction. With this method, free sterol analysis of edible oils is performed by direct injection without the need for prior enrichment of the sample. Keywords: On-line coupled RPLC−GC, Simplex method, direct free sterol analysis, edible oil.