Values for standard enthalpies of formation and dissociation energies for gaseous diatomic monoxides have been selected by critical assessment of experimental data from the literature. Gibbs energy functions, (−(G○T−H○298)/T), and enthalpy functions, (H○T−H○298), have been calculated from literature values for molecular parameters. Computer methods of storage, processing and retrieval are described and the resulting data are given in tables 4 to 11.