The enthalpy of oxidation of La(B 1 − x B′ x)O 3 − δ (x = 0.25 and 0.75 for BB′ ≡ FeCo, MnCo, MnNi and x = 0.2 for BB′ ≡ CoCu) has been derived using solid solution models to analyse thermogravimetric measurements of oxygen non-stoichiometry vs. log( pO 2) at 1273 K. For selected samples the enthalpy of oxidation has also been measured by TG-DSC, and the direct heat measurements agree well with the results from the solution models. The affinity for oxygen decreases when x in La(B 1 − x B′ x)O 3 − δ increases from 0.25 to 0.75. This trend may be extended to a larger range of x-values (x∈[0,1]) when isotherms from the literature are included in the solution modelling. For the materials investigated in this work, the affinity for oxygen decreases in the order Mn 0.75Ni 0.25 > Mn 0.75Co 0.25 > Fe 0.75Co 0.25 (for x = 0.25) and in the order Mn 0.25Co 0.75 > Fe 0.25Co 0.75 > Mn 0.25Ni 0.75 (for x = 0.75). The Co 0.80Cu 0.20 containing material has the smallest affinity for oxygen among all the samples.