Simultaneous imaging of laser-induced fluorescence of toluene and 3-pentanone was used to det. the local abs. oxygen and residual gas concns. present within an engine. The technique utilizes the different sensitivities of the laser-excited mols. to quenching by mol. oxygen as a means to det. quant. images of in-cylinder oxygen concns. The difference in the amt. of oxygen available between two operating conditions was investigated. Results are in agreement with measurements in the exhaust gas.