Method and system for optimizing production from an oil and gas reservoir includes selecting a geocellular grid representing at least one property of the reservoir, defining a data range for the property that reflects uncertainty regarding which values may be used for the property, defining a first reservoir simulation model, simulating production from the reservoir with the model using the at least one property, comparing the output of the simulated production from the reservoir with a predetermined criteria based on historical data, and modifying the property to a different value within the data range for the property if the predetermined historical criteria is not met. These steps may be repeated for at least two values for the property within the data range. The above may be repeated for a second reservoir model and the outputs of the simulated production for the models may then be ranked according to predefined criteria.