A series of Li- and Mg-doped CaTiO3 catalysts were studied and the role of oxygen species, surface basicity, semi-conductivity as well as the mechanism of methyl radical formation were investigated by means of electrical conductivity measurements, oxygen TPD, TP reaction with methane and CH4/CD4 equilibration in relation with the catalytic properties in the oxidative coupling of methane (OCM). A clear relationship between the p-type conductivity, possibly concomitant with anionic conductivity, and catalytic performance was demonstrated, confirming previous hypotheses. Furthermore it was shown that the ability to activate surface oxygen paralleled these parameters. These results combined with the indications yielded by other experiments provided further insights in the nature of sites leading to the selective and unselective reaction.