The conventional water flooding recovers little oil from oil-wet fractured reservoirs. Most of the water passes through the factures and does not imbibe into the matrix due to negative capillary pressures. The goal of this work is to induce wettability alteration on carbonate rocks such that water would be imbibed resulting in oil production. Many anionic surfactants and a few cationic surfactants have been studied. The salinity is adjusted by varying the concentration of sodium carbonate which also increases the pH above the PZC for carbonates preventing adsorption of anionic surfactants on surface. Interfacial tension (IFT) of the order of 10-2 mN/m are observed for anionic surfactants (of the order 1 mN/m for cationic) at optimal salinity. Contact angle studies have been conducted on initially oil-wet calcite plates. Surfactants have been identified which alter the water-oil contact angle to below 90„a. Limited studies with an AFM indicate the removal of adsorbed organics by surfactants. The screened surfactants are used to imbibe the initially oil-wet carbonate cores. The oil recovery is monitored with time. A numerical simulator is developed to understand the process by analyzing in-situ distribution of IFT, flow, capillary pressure, relative permeability and surfactant concentration. The surfactant molecules diffuse from fractures into the matrix and change wettability and IFT. This leads to reduction in capillary pressure and aqueous phase invades from bottom of the core pushing oil out from the top. The change in wettability results in an increase in oil relative permeability which increases oil recovery rate.