Microbial Enhanced Oil Recovery (MEOR) is a technique that uses bacterias and by-products, either as an organic formation damage removing mechanism to increase oil production, or as an agent to reduce residual oil saturation, and eventually increase ultimate recovery factor, specially in mature oilfields. Successful applications reported in Argentina, United States, China and Venezuela were the main driving force to Peruvian local companies, which decided to implement some MEOR Projects in Talara oilfields, with positive and negative results. Consequently, it has been prepared a rigorous analytical and pragmatic methodology by integrating: Well Performance Evaluation, Reservoir Engineering Analysis, Physicochemical Characterization, Rheological Analysis and Sensitivity to Biotreatability Tests. A flowchart including general criteria, as well as, fluid and reservoir properties application ranges was prepared to optimize oil wells and reservoirs selection to MEOR. This flow chart allowed us to recommend two wells of the MEOR pilot project recently implemented in a marginal oilfield of Talara, Peru; preliminary results showed in both wells, improvements in fluid properties (less oil viscosity and higher API0) and initial increase of more than 30% in oil production. Copyright 2009, Society of Petroleum Engineers.