Abstarct: In this study, to evaluate the amount of produced and stored methane in the coal laxyers, several controlling factors of gas adsorption including the quantity and type of organic matter, maturity level, pressure, moisture percentage, and ash content were examined in the coal samples of the Shemshak Formation at the Tazareh region. For this purpose, after sampling from five coal laxyers (K5, K10, K25, P7, P10) in the Tazareh region, organic matter petrography were conducted for determining the constituent macerals, vitrinite reflectance were examined for assessing the maturity level of organic matters, and ash composition and content were determined in each sample. By examining the qualitative parameters of the coals and interpretation of gas adsorption isotherms using volumetric and state equation methods, the controlling factors of gas adsorption were analyzed. baxsed on the results obtained from petrography, total ash content, and methane adsorption analyses, it is revealed that the coals are of the bituminous, rich in vitrinite maceral and the kerogens are of Type III. The analyses showed the two P7 and P10 samples, which have the highest liptinite content, are at the peak of the oil generation window with a hydrogen to carbon ratio greater than one, while the other samples are at the late oil generation and early wet gas phases. Analyzing the methane adsorption isotherms which display pressure versus methane adsorption amount, showed that at pressure more than 30 bar, the slope of curves or the methane adsorption rate for sample P7 increased more than the other samples. Given that higher quality of coal indicates greater gas retention capacity, sample P7, due to its lower ash content and its higher percentages of vitrinite and liptinite compared to other samples, has greatest quality and consequently highest adsorption capacity. Therefore, the rank and quality of the coal affect the shape of gas adsorption curve; as the higher these two parameters, the more rapidly the curve increases at high pressures, until it reaches saturation.