This monograph covers the following topics: 1- Log Derived Saturation Functions For Giant Carbonate Reservoirs in the Middle East. 2- Improved Method for Compositional Modeling using a Fine Scale Geological Description within Gas Injection Pattern in Carbonate Reservoir. 3- Calculation of flowing Bottom-hole Pressure Constraint based on Bubble Point Pressure versus Depth Relationship. 4- Laboratory Studies at Reservoir Conditions on the Impact of Acid Gas and CO2 Displacements on the Carbonate Matrix. 5- Accurate Calculations of Compressibility Factor for Pure Gases and Gas Mixtures.