Gas condensate reservoirs are the categories of hydrocarbon reservoirs. This book is conflated based on the last scientific researches by authors and according to the last books and articles which are published in fundamentals of reservoirs engineering. At discovery, these reservoirs are often in single phase. Initially condensate liquid saturation can build up near a wellbore because of drawdown below the dew point pressure, ultimately restricting the flow of gas. The investigation of production phenomenon is Important in two reasons: First Decreasing gas permeability and in conclusion gas productivity; second condensates have high added value that the production of them in reservoir causes loss of that. In this book the base of used theory for well test data analyzing is expressed in terms of pseudo-pressure, which is an integral over pressure in case of linearization of gas-condensate fluid flow in porous medium.