This study investigates the effects of different parameters on the in-situ gelation of a polyacrylamide/chromium (VI)/thiourea solution using numerical modeling. The effects of polymer rheology, water salinity of the system on polymer viscosity and polymer adsorption, presence of divalent cations (hardness), injection schemes, wettability of the formation, cation exchange capacity (CEC), mobility ratio, and dip angle of the reservoir were investigated by a 3D model using UTGEL simulator. The injection pattern was one quarter of five-spot with eight layers. The model had two thief zones that were located in the middle of the model. The permeability of the thief zones was 1,500 md, with a permeability contrast (heterogeneity) of 15/1. The ratio of vertical to horizontal permeability was 0.01. The results showed that regardless the salinity of the brine, considering both shear-thinning and shear thickening behavior (i.e., UVM model) always yielded better results than assuming shear-thinning behavior only. The results also showed that the higher the salinity of the system, the lower the recovery factor. Thus, low salinity post-treatment water improved the results, especially when the initial salinity of the system was too high. Moreover, the presence of divalent cations (hardness) affected the efficiency of gel treatment; therefore, low-salinity chase water floods improved the recovery. In addition, if the pore volume of the post-treatment water was not high, the optimum injection scheme would be the injection of the polymer solution before the gel treatment. However, if the pore volume of the post-treatment water was high, the ultimate oil recovery would not affected by the injection scheme and the treatment using only the gel would be the most viable scheme. In addition, damage in the low-permeability layer adjacent to the thief zone was significant for oil-wet conditions compared to water-wet conditions. Furthermore, the presence of the clays in the formation (i.e., increasing the cation exchange capacity) lowers the amount of the crosslinkers that are available for polymer to form gel due to the removal of the crosslinkers from the gelant solution. Therefore, no gel will form with a high value of CEC. Increasing the mobility ratio will lower the efficiency of gel treatment; thus, injection of the polymer solution after the gel treatment was the best option. The dip angle from the injector to the producer assisted the gel placement, which resulted in high oil recovery. Finally, the effect of the skin factor should be taken into consideration in designing the gel treatment, especially at high injection rate.