Produced water from crude oil production process is imbued with various contaminants which makes it unsafe for discharge into the environment without adequate treatment. The weight fractions of these contaminants vary from one well to another depending on the nature of the well, its age and production conditions. The discharge of produced water is subject to treatment which is usually aimed at reducing the weight fraction of the polluting components to a level considered safe for the environment by the regulator. The cost of treatment of produced water is prohibitive and surges as the age of the well increases and the reservoir characteristics change. The concentration of these pollutants (Benzene, Toluene, Phenol, Ammonia etc) in produced water could be altered by adjusting the production variables of temperature, pressure, residence time and flowrate. This paper has presented the results of simulation using HYSYS 6.2 to show that combination of temperature and pressure could decrease the concentration of the selected pollutants in produced water. This outcome is very important in oil and gas production in meeting regulatory limits for discharge of produced water and in the reduction of the cost of treatment of produced water.