In this work, a rich premixed gasoline/O-2/Ar flame at low pressure (30 Torr) with an equivalence ratio (phi) of 1.73 is investigated and reported. The identification and mole fraction calculation of most flame species, including isomeric intermediates, are performed in this study using the tunable synchrotron photoionization and molecular-beam mass spectrometry techniques, and the flame temperature profile is recorded using a Pt/Pt-13%Rh thermocouple. The possible formation pathways of some flame species, such as 1,3-butadiene, benzene, and naphthalene, are discussed in this paper, along with the comparison between this flame and other premixed hydrocarbon flames. It is concluded that the mole fraction of 1,3-butadiene is strongly related to that of the 1-buten-3-yl radical in the hydrocarbon flames. The decomposition of higher aromatics is found to be more important for benzene formation in this flame than the recombination of small intermediates, while the intermediate reactions are suggested as the dominant formation pathway of naphthalene. The comprehensive experimental data will be helpful for understanding the combustion mechanism of gasoline and pursuing a better control of exhaust emission levels from gasoline-fueled engines.