Microbial Enhanced Oil Recovery (MEOR) is a promising EOR technique. Feeding bacteria so that they can be stimulated to produce metabolites is a good way to increase recovery factors. In this paper, we present a mathematical model which describes a MEOR process and can be applied to estimate the recovery factor.A one-dimensional isothermal model, comprising displacement of oil by water containing bacteria and nutrients, is studied. The model is composed by a hyperbolic system of four partial differential equations with source terms and appropriate initial and boundary conditions, solved numerically by a fractional step method. We analyse the case when the produced metabolites are biopolymers which increase water viscosity, and then, improve sweep efficiency.The required parameters used in this model are not always known, therefore, to better investigate their importance, a sensitivity analysis is run and the impact in the recovery factor observed. The sensitivity analysis was performed according to the following steps: 1) three values for the maximum specific growth rate were assumed and their impact in the recovery factor is analyzed, to demonstrate the importance of bacteria screening; 2) water viscosity dependence on biopolymer concentration is described by three functions and the resulting recovery factor of each one of them is compared; 3) three different models describing bacteria growth and their effects in the recovery factor are also presented. Maximum specific growth rate was the parameter that has caused the major impact in the recovery factor. When a small value was adopted, there was no additional oil recovery in comparison to water injection. This sensitivity analysis has shown the importance of laboratory tests to improve the prediction of recovery factor. It was also noticed that a significant incremental oil recovery can be achieved with this process of MEOR for different oil viscosities.