Standard enthalpies of formation at 298.15K, ∆fH298.15○, for RCoO3-δ (R = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y) perovskite-type rare-earth cobaltites were obtained from the combined results of drop and reduction calorimetry. The relationship between the oxygen nonstoichiometry, δ, and thermodynamics of RCoO3-δ was discussed. The fact that RCoO3-δ with smaller ionic radius of R3+ tend to be less stable, having more positive enthalpy of formation from binary oxides (CoO and R2O3), ∆f,oxH298.15○, was confirmed for all the studied RCoO3-δ. Drop calorimetry results were also used in discussing, comparing and assessing the literature heat capacity, CpT, data for RCoO3-δ (R ≠ Y). For YCoO3-δ, both ∆fH298.15○ and CpT were obtained for the first time solely from the drop calorimetric results; ∆fH298.15○ values determined by two different methods perfectly agree with each other. The reference data and CpT of RCoO3-δ were used to calculate ∆fH298.15○ from the published EMF measurement results so as to compare the available ∆f,oxH298.15○(RCoO3-δ) values. An unusual dependence of∆fH298.15○(LaCoO3-δ) on its heat treatment history was identified and supported by the additional isoperibolic solution calorimetry measurements.