Abstract Hydrocarbon solvent injection into preheated reservoirs has been suggested as an alternative to sole injection of steam or solvent for heavy-oil recovery. But, this is a highly pressure and temperature sensitive process. This paper investigates this process through a numerical modeling exercise and formulates the optimal pressure and temperature conditions for maximized recovery and minimized asphaltene precipitation. We first report the results of numerical simulation of laboratory experiments, in which heavy-oil was exposed to solvent vapor at high temperatures. To achieve these results, a radial 3D numerical model of 15×1×48 cells was constructed using a commercial numeric simulator. The injection of either propane or butane into sand packs or consolidated sandstones at elevated temperatures was simulated. A pressure–temperature sensitivity analysis was carried out for different core sizes to understand the dynamics of the gravity drainage process associated with asphaltene precipitation. Asphaltene pore plugging behavior was modeled and diffusion of solvent into the heavy-oil was analyzed to determine both ideal solvent type and optimal operating conditions for propane or butane injection in a temperature range of 52–112°C. Our results and observations showed that the solvent should be in the gas phase and its sensitivity to temperature and sample height (for effective gravity drainage) is more critical than the pressure. There also exists a critical temperature that yields a maximum recovery and this value was determined for the rock/reservoir types and solvents considered in this study. Solvents considered, i.e., propane and butane, behaved differently in terms of asphaltene precipitation and its effects on ultimate recovery.