Wettability of subsurface reservoir rocks is a key parameter that influences multiphase flow characteristics of the fluid-rock system, including relative permeability, capillary pressure, saturation distribution, and displacement efficiency. To investigate such effects, various techniques have been implemented to change wettability, including nanoparticle injection, chemical treatment, surfactant injection, brine salinity adjustment, etc. However, most studies have focused on the use of model surfaces (e.g., mineral surfaces) and not actual rock samples, which are far more representative of real-world application. The ability to modify the wettability of the pore space in the reservoir has implications in a range of areas, such as reducing/preventing water/condensate banking around hydrocarbon production wells, CO2 geo-sequestration, enhanced hydrocarbon recovery, and separation of CO2 using porous media. In light of the above findings, in this research, we primarily explored supercritical fluid-based silane surface modification of quarried sandstones (i.e., Gray Berea, Upper Gray Berea, Bentheimer, and Bandera Brown). Using high-throughput treatment methods, these samples were treated with five different silanes and then characterized using X-ray photoelectron spectroscopy and contact angle measurements. Conventional techniques for depositing silanes onto a surface from organic solvent (i.e., toluene) were also conducted for comparison. In all of the cases studied, our experimental results show that, when supercritical CO2 (scCO(2)) is used as a carrier for the silanes, improved surface coverage and wettability alteration were achieved in comparison to when the conventional solvent (e.g., toluene) is used. As a result, the wettability of sandstone surfaces as measured under high- pressure conditions was altered significantly from strongly water-wet (theta approximate to 11 +/- 5 degrees) to strongly non-water-wet (theta approximate to 145 +/- 6 degrees). Furthermore, we showed that scCO(2) at even relatively modest reservoir conditions (10 MPa at 60 degrees C) could be used rather than toluene for application in real-world scenarios; this reduces environmental and safety concerns significantly.