Five Au–Ga alloys have been studied using x-ray photoelectron spectroscopy as part of the program to determine alloy effects on core level binding energies and identify thin film and bulk compositions of unknown AuxGay alloys. The binding energies and peak intensities of the Au 4f, Ga 2p3/2, Ga 3p3/2, and Ga LMM core levels were determined for pure Au and Ga along with bulk alloy compositions of α-Au0.88Ga0.12, β-Au0.78Ga0.22, γ-Au9Ga4, AuGa, and AuGa2. These values were determined for surfaces scraped in situ to expose the bulk composition. The Au 4f7/2 binding energies were 83.95 eV for pure Au and 84.4, 84.6, 84.9, 85.2, and 85.5 eV for each of the respective alloys, while the Ga core levels and Auger energy shifted less than 0.3 eV over the range of alloy compositions. These results exhibit the same trend as the previously studied Au–In system and furnish calibration values that allow determination of the composition of unknown alloys.