This paper presents the application of a fiber optic sensor based on bifurcated fiber bundles; in the bifurcated design, separate fibers carry the excitation and emission radiation. The physics principle is simple, the fraction of light transmitted between the receive elements in the bundle and the transmit elements in the bundles depends of the light wave passes through the gasoline; three fuel-adulterant mixtures in different proportions by volume were prepared and individually tested. The high sensitivity of laser, and the versatility of fiber-optic technology and experiment proved that the system has simple construct and high sensitivity during absorption on a transition process.