Further evidence was delivered that certain impurities, which Could be contained in MgO samples, might be responsible for observed variability in MgO basicity and catalytic performance in oxidative coupling of methane. The Surface basicity/base strength distribution of a series of MgO samples containing or not containing Ca and Na impurities was determined by a temperature-programmed desorption of CO2. It was revealed that samples containing Ca and Na impurities have much more medium, strong and very strong basic sites. The surface basicity of MgO samples containing added alkali or alkaline earth compounds or water was characterized by a test reaction of transformation of 2-butanol. It was confirmed that the introduction of these compounds to a pure MgO enhanced both its basicity and activity in oxidative coupling of methane. (C) 2002 Elsevier Science Ltd. All rights reserved.