A gasoline-fueled engine is a major source emitting toxic compounds. It is important and necessary to detect and identify these exhaust emissions from engines. The gasoline combustion process in engines approximates to a premixed flame. In this experiment, a lean premixed gasoline/oxygen/argon flame at 2.00 kPa with an approximate fuel equivalence ratio (phi) of 0.75 has been studied with tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam sampling mass spectrometry. About 80 species produced in the flame have been unambiguously identified by measurements of the photoionization mass spectrum and photoionization efficiency ( PIE) spectra. In addition, mole fraction profiles of these species are derived at the selected photon energies near ionization thresholds, and the temperature profile was measured with a Pt/Pt-13% Rh thermocouple. Combined with the mole fraction profiles, the formation mechanism of some important radicals, oxygenated compounds, and stable intermediates are analyzed in detail.