A number of gaseous oxyacid salts have been identified by Knudsen effusion mass spectrometry by vaporizing In2O3 from molybdenum or tungsten double two-temperature cells. The stability of gaseous molecules In2MoO4, In2WO4, and In2W2O7 was deduced from the measurements. The structures and molecular parameters of all investigated salts were obtained using quantum chemical calculations. On the basis of equilibrium constants measured for gas-phase reactions, the standard enthalpies of formation were determined to be -855 ± 33, -773 ± 30, and -1565 ± 30 kJ mol(-1) for In2MoO4, In2WO4, and In2W2O7 respectively. Overall the results obtained allowed us to estimate the standard formation enthalpy of In2MoO3, In2WO3, and In2Mo2O7 to be -519, -467 and -1530 kJ mol(-1), respectively, with an accuracy of ±40 kJ mol(-1).