Water is present in most shale reservoirs and has a negative effect on methane adsorption. A modified Langmuir model was developed to model methane adsorption on wet shales. This model was validated against published adsorption data on wet shales. We also studied the effect of adsorbed water on methane adsorption. The Langmuir pressure increases with increasing water content, which could be explained by the fact that absorbed water molecules weaken the methane-shale interaction and reduce the mobility of adsorbed methane molecules. The maximum methane adsorption capacities of all investigated samples decrease approximately linearly with increasing water content when the water saturation is lower than 70%. The methane adsorption capacities of wet shales are controlled by TOC content, kerogen maturity, and the content of clay minerals, which is due to the fact that adsorbed water molecules have a large impact on the methane adsorption capacities of clay minerals but little effect on that of high maturity kerogen. The hydrophobic fraction of organic matter is a primary control on methane storage by adsorption under reservoir conditions.