Since the discovery of the Pre-Salt layer in Brazilian waters, production of high gas-oil ratio (GOR) has increased considerably. This gas has a high content of water, CO2, and sometimes H2S. A study in different conditions was conducted using several equations of state (EoS) such as Peng-Robinson, GERG-modified Peng-Robinson (PR-ISO-04), Soave-Redlich-Kwong, and Cubic Plus Association (CPA). Petrobras Process Simulator has been used to perform the phase equilibrium calculations. All the EoS except for CPA used parameters from the literature. A new parameter estimation procedure for CPA has been proposed using a particle swarm optimization algorithm followed by the SIMPLEX method presenting themselves together as an optimal approach. The results show that PR-ISO-04 can be considered to be an improvement compared to the original Peng-Robinson but CPA appears to be the most promising approach to be used for predicting dew points for water-containing mixtures, especially at high pressures.