Figure 5.  Methane partial pressures (blue circles) where exsolved gas is drier than the reservoir gas.  The difference in methane partial pressure is less than the difference in total pressure (red circles). The methane partial pressure of a wet gas in the reservoir may be less than that of exsolved gas above the seal.  In this example, the total gas overpressure (P) is positive, but the methane gas overpressure (P*) is negative.