Abstract Lisama is an oil field operated by ECOPETROL S.A. located in the east side of Middle Magdalena Valley basin in Colombia. The reservoir is a stratigraphic-structural combined trap and the oil comes from the Tertiary, mainly from the formations Mugrosa and Colorado. A methodology of Integrated Fluid Analysis is applied. The methodology includes fluid sampling analysis, PVT test quality control and reservoir fluids representativeness. Then, a cubic Equation of State is developed to match the best PVT data. Finally, compositional gradients are built so that they can describe properly the variation of PVT properties with depth. There are 16 PVT studies in Lisama Field. However, after applying the procedure described above, only the results from four PVT reports are found to be both reliable and representative. Afterwards, Peng-Robinson Equation of State is fitted against PVT depletion data applying a non linear regression technique in order to change systematically internal parameters of the equation of state such as binary interaction coefficients, critical pressures, critical temperatures, volume shifts, and critical Z factors. Finally, isothermal compositional gradients based on reliable compositions are built and a gas-oil contact (GOC) analysis is developed. The results obtained by applying this methodology indicate that fluids in Lisama field's northwest sector, known as the Corridor of Gas, have a different behavior in comparison with those of the remaining area, particularly in relation to the location of the respective gas – oil contacts. That is, the two GOC values predicted for the fluid system in the Corridor of Gas are located within the Mugrosa formation, while the GOC value for the fluids of the remaining area are predicted out of this formation. Therefore, this would mean that the corridor of Gas is isolated from the rest of the Lisama area. This study is a fundamental support for the initialization of the reservoir simulation model and the prediction of new development strategies that would lead to optimize the recovery of fluids in the area.