The methane sorption capacities of the dry shales show a positive correlation with TOC but significant deviations from this trend exist for individual samples. The TOC-normalized sorption capacities correlate positively with maturity in terms of Vitrinite Reflectance (VRr) up to a certain value of VRr (~ 2.5%) above which an opposite trend is observed. No correlation was observed between the clay content and the TOC-normalized sorption capacity to methane, indicating that clay minerals do not significantly contribute to methane sorption in these organic-rich shales. The shape of the excess isotherms changes systematically with temperature and maturity. The Langmuir pressure (pL) increases exponentially with temperature and follows a negative power-law trend with maturity. Compared to dry samples, the sorption capacity in moisture-equilibrated samples (at 97% RH) is reduced by 40 to 60%. No difference is observed between 97% and 75% RH, indicating that the critical moisture content is at or below 75% RH. The monolayer sorption capacities for water obtained from the GAB fit are 0.5 to 3 times those for methane, derived from the Langmuir fit. There is a weak positive correlation between the methane and the water sorption capacity, suggesting that methane and water molecules share some of the sorption sites and these reside partly within the organic matter.