Natural gas compositions and their relationship to thermodynamic equilibrium. Histogram of log Q (Q = [(C1)*(C3)/(C2)2]) for 1600 gas compositions obtained from the U.S. Department of Interior; mean log Q = 0.90 ± 0.43 . Hydrocarbon concentrations used to calculate log Q were % vol C1–C5. These gases do not include compositions with C2 or C3 < 0.5% vol. Since concentrations were rounded off to the nearest tenth in the DOI database, values in that range introduced substantial errors in calculating Q. The vertical dark lines and the horizontal bar are defined in Fig. 4.