In this Book, the Eclipse 300 reservoir simulator software was used to perform compositional simulation of Sarkhoon gas condensate reservoir (well No.4) In Iran and investigate the gas injection and gas recycling phenomena for enhanced condensate recovery. Different scenarios of gas injection and gas recycling at current reservoir pressure and at abandonment pressure had been considered using different production and injection well constrains and different gas compositions. Also, natural depletion and gas injection processes had been modeled at experimental scales for different core lengths with different production and injection flow rates in both vertical and horizontal cases. Some experimental data were used to tune the Peng-Robinson EOS with the help of PVTi software. In order to select appropriate correlations for generating critical properties and acentric factors of pseudo-components, a comparison was made between different sets of most widely used correlations by simulating the PVT experiments done on SA4 well fluid. Also, different cases of reservoir modeling have been compared to investigate the effect of various parameters on gas and gas condensate well production rates.