The present work numerically investigates the effect of reservoir temperature and pH on microbial growth and its transport within the reservoir which undergoes the reversible sorption kinetics. Further, the present work also studies the influence of reservoir temperature and pH on changes in interfacial tension between oil and water, capillary pressure and its impact on microscopic oil displacement efficiency. The microbe used is strain of Bacillus sp and the nutrient supplied to microbe is molasses. For this purpose, a novel mathematical model is developed which describes the coupled multiphase fluid flow and multispecies reactive transport in porous media which occurs during the MEOR process. Moreover, in the present work, the first order Monod kinetics equation is expressed as a function of temperature and pH which dictates the microbial growth rate. The developed mathematical model is sloved numerically by finite volume discretization technique and the results are found to be numerically stable and validated with the experimental results. The numerical data used for validation and for numerical simulation studies are presented. The results suggest that the oil displacement efficiency increases as the reservoir temperature and pH approaches the optimum temperature and pH required for microbes to reach its maximum growth. The present numerical model may be applied as an effective screening tool before the application of MEOR process and also serves as a reservoir simulator tool to predict the performance of MEOR process. Copyright 2015, Society of Petroleum Engineers.