Vaporization of the LaCr1-xMgxO3-delta perovskite phase (x=0.03, 0.09, 0.14) and the two-phase sample {MgO+MgCr2O4} was investigated by the use of Knudsen effusion mass spectrometry in the temperature ranges of 1950-2050 and 1750-2080 K, respectively. The partial pressures of Cr(g), CrO(g), CrO2(g), Mg(g) and LaO(g) were determined for all the samples investigated. The partial pressure of O-2(g) was evaluated from equilibrium reactions in the gas phase. The ion intensities were used to calculate the thermodynamic activities of the system components at 2000 K. The Gibbs energies of formation of LaCr1-xMgxO3(s) at 2000 K resulted from the thermodynamic activities as -87.4 +/- 5.5 kJ mol(-1) (for x=0.03) to -91.5 +/- 3,8 kJ mol(-1) (for x=0.14). The results are compared with thermodynamic data of undoped LaCrO3(s). The Gibbs energy of formation of MgCr2O4(s) at 2000 K amounts to -42.4 +/- 0.9 kJ mol(-1). Implications of the present data for the potential use of the material in SOFC technology are discussed.