At low pressure, up to 10 bar, the gas behavior of CH 4 is ideal. This translates into the departure function being almost 0. At higher pressures, the departure function decreases until it reaches a minimum at around 500 bar (-4 kJ mol -1 ). It then increases again to reach a value of 0 at around 2.000 bar. Finally, the departure function keeps increasing monotonically until it becomes very positive. However, very few points lie in that range