Extensive grand canonical Monte Carlo simulations are performed for the calculation of the amount of methane gas that can be stored inside the hydrate structure sI focusing on temperature and pressure conditions that are of interest to practical applications (e.g., methane storage/transportation, methane hydrates in nature). Langmuir-type "absorption isotherms" are used in order to present the results for methane in the cages of the hydrate structure. In particular, the methane content inside the different type of hydrate cages is given as a function of pressure, where the parameters of this function are temperature-dependent. A comparison between available experimental data for cage occupancies and calculated values resulted in good agreement. The correlation between chemical potential and pressure is determined through NVT Monte Carlo simulations. Simulations are performed for the TIP4P/Ice water model and two methane models (United Atom and All Atom). The calculations of the current study can be utilized during the process of refining the estimates of methane gas "in-place", in hydrate deposits, when pressure and temperature conditions at the hydrate reservoirs are known. A discussion on the implication to geologic media containing hydrates is also presented.