The phase equilibria in the ternary Ca–Co–O system have been studied by thermal analysis (DSC/DTA, TGA), X-ray diffraction of quenched samples and low temperature heat capacity measurements. These experimental data were combined with the data available in literature and used to assess the thermodynamic quantities of the involved phases. A particular focus was put on the misfit cobaltite Ca3Co3.93O9.36 as a potential candidate for high temperature thermoelectric conversion whose observed nonstoichiometry was described in terms of compound energy formalism. The phase diagram was mapped using FactSage program.