Abstarct: study of gas condensate reservoirs are challenging cases in petroleum engineering. Commonly production from this reservoir without pressure maintenance makes high gas production and relatively small condensate production. Decreasing reservoir pressure and reaching to dew point pressure cause increasing condensate saturation in reservoir that is not desire. Such growth in Condensate saturation produces two major problems: Decreasing gas production and gas relative permeability and Condensate will trap in reservoir so that in some cases will not be recoverable. South Pars field is one of the largest gas fields in the world and due to high gas extraction in recent years, reservoir pressure is reaching to dew point pressure; therefore it is important to Investigate different scenarios for pressure maintenance in this field. Given that South Pars field in iran is shared with North field of Qatar, To protect national interests, using pressure maintenance methods are vital and Requires a comprehensive and accurate study. In this thesis, after studying and simulating the South Pars gas field, In order to choose the best EOR scenario which results in the lowest waste of condensate and Increase the recovery factor, different scenarios of production and injection have been investigated. 〖CO〗_2, N_2 and output gas of separator have been selected for injection. Eclipse 300 compositional simulation software is used for reservoir modeling and simulating. results showed that restoring output gases of separator (gas recycling) is the best scenario to solve the gas condensate reservoirs problem. It was also observed that the best time for EOR process is coinciding with the start of production and before pressure reduction to dew point pressure; and the location of injection wells is an affecting factor on improving performance of gas injection process.