Carbonate reservoirs pose unique challenges to the petroleum industry. Research during the last decade has shown the potential for application of principles of nanoscience and technology toward solving a variety of problems faced by the petroleum industry today. The authors investigated the effectiveness of nanofluids of silane coated silica nanoparticles as in situ reservoir agents. Effects of salinity of dispersing medium and concentration of nanoparticles on particle size and surface zeta potential were studied to characterize the stability of nanofluids. Carbonate core samples were taken from an Indian carbonate reservoir and their wettability was restored. Contact angle measurements were made before and after the application of nanofluid to investigate the alteration in wettability. Particle size measurements showed agglomeration of nanoparticles. It was found that the extent of agglomeration was affected by salinity of the dispersing medium and concentration of nanoparticles. Wettability studies indicated that nanofluids of silane coated silica can affect wettability change toward a more water wet state. Around 2 g/L was found to be the optimal concentration for affecting wettability change. Copyright © Taylor and Francis Group, LLC.