a disclosed method for characterizing gas adsorption on a rock sample includes : measuring a nuclear magnetic resonance response of the rock as a function of surrounding gas pressure along an isotherm ; transforming the nmr response to obtain a langmuir pressure distribution of gas adsorption on the rock sample ; and displaying the langmuir pressure distribution . the langmuir pressure distribution may be shown in one dimension , or may be combined with additional pressure - dependencies such as spin - lattice relaxation time , spin - spin relaxation time , and chemical shift to form a multi - dimensional distribution . the method can further include : identifying peaks in the langmuir pressure distribution ; and associating a gas storage mechanism and capacity with each peak . it may still further include : exposing the rock sample to a treatment fluid to obtain an altered sample ; repeating said measuring and transforming operations with the altered sample ; and comparing the langmuir pressure distributions to determine effects of the treatment .