Two compounds, BaLa2Fe2O7(s) and BaLaFeO4(S) in the quaternary system Ba-La-Fe-O have been prepared by citrate-nitrate gel combustion route and characterized by X-ray diffraction analysis. Heat capacities of these two oxides were measured in the temperature range from 302 K to 832 K using a heat flux type differential scanning calorimeter. Two different types of solid-state electrochemical cells with CaF2 as the solid electrolyte were employed to measure the e.m.f. as a function of temperature. The standard molar Gibbs energy of formation of the above oxides was calculated as a function of temperature from the e.m.f. data. The standard molar enthalpy of formation at 298.15 K, Delta(f)H(m)degrees (298.15 K) and the standard entropy S., (298.15 K), of these two oxides were calculated by second law method. The values of Delta(f)H(m)degrees (298.15 K) and S., (298.15 K) obtained for BaLa2Fe2O7(s) are: -3446.4 kJ (.) mol(-1) and 246.6 J (.) K-1 (.) mol(-1) whereas those for BaLaFeO4(s) are: -2080.4 kJ (.) mol(-1) and 95.0 J (.) K-1 (.) mol(-1), respectively. (C) 2004 Elsevier Ltd. All rights reserved.