Asphaltenes may generate production loss in oil reservoirs, because of several factors related to the interaction between the asphaltene molecules, aggregates, and the reservoir rock. Consequently, this could alter the wettability of the rock surface, increase the viscosity of the crude oil, and reduce the permeability of the porous media. In a previous study, we have developed the solid-liquid equilibrium (SLE) model based on Chemical Theory to describe the adsorption behavior of asphaltenes onto porous and nonporous solid surfaces. However, the SLE model neglects the effect of pressure on the interactions of asphaltene-asphaltene and asphaltene-aggregate-solid surfaces of the reservoir rock primarily under reservoir conditions (RC). Thus, in this study, to account for the effect of pressure, a modification to the previously developed SLE equation is presented. In this study, a novel and original model-called the SLE-RC model of adsorption-has been proposed to describe the adsorption mechanism mainly under reservoir conditions, for which the pressure and temperature effect has been evaluated. This model describes the temperature-pressure-dependent adsorption isotherms with five parameters: the maximum amount adsorbed, the constant of the i-mer reactions, Henry's law constant, the molar volume, and the solubility parameter of the asphaltenes. The proposed model has been validated with adsorption tests on porous media under flow conditions at different pressures and temperatures. The dynamic adsorption experiments were performed at different asphaltene concentrations (100-2000 mg/L), pressures (6.89-17.24 MPa), and temperatures (313-353 K). The SLE-RC model was successful validated using more than five experimental data describing the adsorption isotherms of the asphaltene onto a packed bed of silica sand at high pressure and temperature and following a Type III behavior with root-mean-square errors (RMSE%) below 2%. In addition, the packed sands used in the adsorption tests were analyzed based on surface and color changes using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) analysis, and polarized light microscopy (PLM); the results were in agreement with the SLE-RC model parameters.