This course covers the fundamental knowledge a petroleum reservoir engineer needs to know in providing a qualitative and quantitative description of a hydrocarbon reservoir and how to manage its performance. The course will start with several of the well-established physical property correlations for the reservoir fluids such as natural gases, crude oil systems, and reservoir water systems. The course then will investigate the mathematical relationships that are designed to describe the flow behavior of the reservoir fluids. Volumetric reservoir estimation methods, derivation of material balance equations, Applications of material balance to predict the performance of oil and gas reservoirs and Decline curve analysis methods will also be described in the course. Finally, course will end wih introduction to water influx and some basic calculations related with it.