Condensation in raw biogas during compression is a problem because the CO2, water and H2S in the liquid phase is very corrosive. Raw biogas typically contains 60 mol-% methane, 40 mol-% CO2, is saturated with water and may contain contaminants as H2S. Under compression up to 300 bar, it is a question whether condensation (mostly water) will occur. In case of H2S, it is of interest whether it has influence on the dew point temperature. It is also of interest how much H2S will condense in the liquid phase. The aim of this work is to calculate the dew point or condensation under different conditions with varied temperature, pressure and gas composition and using different equilibrium models. Phase envelopes are calculated which show the two-phase area for temperature and pressure for a specified composition. Traditionally, gas mixtures of methane, CO2, H2S and water are calculated with standard models like Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK). There is traditionally only one constant binary parameter for each component pair. Earlier evaluations indicate that this may increase the accuracy of condensation detection. Other models are also available in Aspen HYSYS. For mixtures of methane and CO2 with up to 1 mol-% H2S (a high value for biogas), the different models gave similar results. Under normal ambient temperatures (above 0 °C), a mixture with more than 40 mol-% methane will not give any condensation. When the H2S increased from 0 to 1 mol-%, the dew point temperature increased with only 1.0 K. When raw biogas is cooled or compressed, water will condense first. Some H2S will dissolve in the water, and the amount of calculated H2S dissolved in water varied slightly with the model and on the selected binary parameter for water/H2S. For biogas simulation, it is recommended to select a binary parameter that fits the experimental data for H2S solubility in water.