The use of uncertainty analysis as a tool in reservoir studies is becoming more and more common inside Petrobras and all around the world. However, in fields with production history, traditional uncertainty analysis, combining possible values of uncertainty variables, can lead to models that poorly represent the reservoir and to results that do not respect the available dynamic data. During uncertainty analysis process, history matching evaluation can considerably reduce the existing uncertainties.The methodology used in this work is based on experimental design and response surfaces. Besides the cumulative production response surface, another one is generated to represent the quality of the history matching. Only cases with a good history matching are selected as input to the Montecarlo simulation. With this technique, it is possible to evaluate the initially defined probability distributions and, if necessary, to redefine shape or limits for the probability density curve.The methodology was applied in a real study in Petrobras. There are uncertainties related to faults, absolute permeability and also related to the existing fluid properties. Although there are other wells in the same block, the studied area is located in a sea-bottom slope region, where water depth varies considerably within the block, possibly influencing the oil quality.Since there are two wells operating in the studied region, one producer and one injector, the developed analysis took the existing dynamic data into account, reducing model uncertainties. IntroductionThe field in study is located in Campos Basin. It comprises around 150 km 2 in area and the water depth varies from 800 m to 2000 m. There are zones in production of different geological ages, from Oligocene to Miocene.The development project contains around 30 wells, comprising producers and injectors. The well location plan was developed in order to maximize the drainage of the several compartments, minimizing gas-oil ratio and to postpone water breakthrough.After a few years in operation, with the production decline, some new locations have been studied in order to take advantage of the remaining platform capacity. The target study is located in a region with uncertainties related to faults existence, rock permeability and also related to fluid properties. Although there are drilled wells in this same block, the aiming area is located in a sea bottom slope region, so the water depth varies considerably along the block, possibly influencing the oil quality.In the studied region, there are two operating wells (a producer and an injector well), both horizontals. Once production history exists in this block, the analysis took in account the existing dynamic data. Traditional uncertainty analysis, combining possible values of uncertainty variables, can lead to models that poorly represent the reservoir and to results that do not respect the available dynamic data. During uncertainty analysis process, history matching evaluation can considerably reduce the existing uncertainties.