The properties and the role of MgO in oxidative coupling of methane to C2+ hydrocarbons (OCM) have been studied. The transformation of 2-butanol over several unpromoted MgO samples was applied as a test reaction for the determination of the surface basicity/acidity. The specific rates of alcohol transformation and of product formation were determined in a flow silica reactor at 608 +/- 1 K. All the investigated MgO samples exhibited significant dehydrogenation activity and extremely weak dehydration activity, producing 2-butanone as the main product and only minor or even negligible amounts of butenes. The samples of MgO containing Ca compounds as impurities showed enhanced basicity, as concluded from the higher rates of ketone formation and from the presence of solely 1-butene among butenes. These samples also showed enhanced catalytic performance in the OCM process. The surface basicity of MgO, affected by the content or the absence of some impurities (Ca, Na, etc. oxides), was recognized as the decisive factor responsible for observed diversity in the catalytic performance of MgO in OCM, more significant than other surface properties or precursors. (C) 2002 Published by Elsevier Science B.V.