Oil recovery by water flooding from carbonate reservoirs is considered ineffective because of the capillary forces in naturally fractured oil-wet carbonate formations. Surfactant solutions are often recommended to enhance the oil recovery by both wettability alteration and reduction of interfacial tension (IFT). In this study, the effects of cationic surfactants from the trimethylammonium bromide (C_nTAB) family, viz., C₁₀TAB (BTAB), C₁₅TAB (DTAB), C₁₆TAB (TBAB), and C₁₉TAB (CTAB), on the surface tension, IFT, and wettability alteration of a carbonate rock along with adsorption of the surfactant on the carbonate rock were investigated. Different analyses, including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDAX), and Fourier transform infrared spectroscopy (FTIR), were conducted to study the mechanism for wettability alteration of the oil-wet carbonate surface. Results demonstrated that, among the four surfactants used, C₁₅TAB and C₁₉TAB presented a better effect on reduction of the surface tension, IFT between oil and water, and wettability alteration of the oil-wet carbonate rock surface. Adsorption of surfactants on the carbonate rock was studied, and the results were analyzed by Langmuir and Freundlich models. A comparative study of FTIR analysis of crude oil and rock in the presence of different surfactants was performed to investigate the interactions between different phases.