Crude oil is produced from oil reservoirs contain water, gas, salt, sediment and small amounts of metals are, for the preparation of this fluid for export refineries that produce food products can be separated gross be water to Isolation crude oil and gas in the Vessel called separator is used most commonly used three-phase separators are horizontal, multi-stage operation is performed during the first stage of separation near the oil tanks do be called the wellhead separators are known. Software has been studied to implement content Aspen Hysys 2006 software is used, it is considered a horizontal three-phase separator , the results indicate that differences in the number of parameters low Mddvdy and in most cases is negligible for low margin is proposed .