There are a plenty of reasons to validate (history match) the reservoir simulation model.Without history matching a robust future production forecasting is not possible. Historymatching process is an important part of the reservoir engineering. It can be applied usingmanual history matching approach or assisted history matching approach. As a process itselfhistory matching is time consuming and it needs to be done by experienced reservoirengineer. Regarding the technology improvement during the years history matching hasbecome automated. Assisted history matching is widely used because it decreases the usedamount of time and gives relatively good results for improving the quality of the reservoirmodel. Some of the uncertainties related with the history matching process are based onlimitations of simulators (related to its specifications) and others are provoked from limited orlack of data for validation. Despite all these difficulties reservoir simulation is one of the basictools for oil and gas field development. The set of data (input and output) which isincorporation between data evaluations and interpretation into simulator is the reservoirmodel. Geological reservoir model is used as an input for numerical simulator after properupscaling of simulation grids. Geomodel grid represents the details like structural features(surfaces, faults), distribution of petro-physical properties throughout the volume of reservoir.Upscaled reservoir model keeps the accuracy of geomodel but with upgraded number of gridcells which make it easier to run simulation. Reservoir model is constructed by implementingof diverse sources of data, which characterize reservoir and fluid properties. Static parameterslike porosity and permeability, and dynamic variables such as pressure and fluid saturation arereservoir properties whose authenticity has a great importance for the reservoir model.Reservoir simulation model should be geologically realistic and also account for a lot ofdifferent measurement scales. Reservoir simulation reflects the transport processes of thefluids in the reservoir.