The adsorption of surfactants on reservoir rock has been known from early studies on surfactant flooding for this purpose, Adsorption mechanism of new nonionic surfactant on carbonate rock surface is not yet reported in the literature. This paper describes adsorption of a new nonionic surfactant which extracts from Zizyphus spina christi onto porous real carbonate reservoir rock has been studied by examining adsorption behavior in a system of solid phase carbonate and of an aqueous phase of surfactant. Effects on surfactant adsorption density for different surfactant concentration were conducted in batch system. The studies were conducted at 28 degrees C. For the crushed rock, the equilibrium time was approximately one day. Adsorption of surfactant was assessed using a conductivity technique for aqueous phase. The rate of adsorption dependent on availability of surfactant in the system, it was found that the adsorption of surfactant increased with increasing surfactant concentration. Adsorption data for sub-micelle concentration were found to fit successfully Freundlich isotherm. The investigation is instructive for surfactant selection for enhanced oil recovery (EOR). (c) 2012 Elsevier Ltd. All rights reserved.