A GLC-acid extraction method is described for the determination of MTBE in gasolines. The method consists of a programmed GLC analysis starting at about room temperature conducted before and after extraction with cold 85% phosphoric acid. This treatment results in the preferential solubility of ethers and other oxygenated compounds while minimizing the reaction of olefins and aromatics which may be present in the gasolines. Plotting various known concentrations of MTBE in gasolines against the concentrations determined in the same samples by our methodolgy results in a straight line relationship. The concentration of MTBE in any sample of gasoline may thus be determined using our GLC extraction procedure and the calibration line. The analysis can accomodate a wide choice of standard GLC columns and programs.