Adsorption storage is the most promising low-pressure alternative for storing natural gas, but some operational difficulties hinder the success of this technology. From a modeling perspective, this article addresses the impact of gas composition on the cyclic behavior of adsorptive natural gas storage systems. The cyclic operation of an onboard storage reservoir is modeled as a series of consecutive two-step processes, each consisting of charge with a fixed composition gas mixture followed by discharge at constant molar flow rate. Special attention is,given to the composition and calorific value of the gas deliver ed by the storage system and to performance quantifiers that measure net deliverable capacity as a function of cycle number Evidence of a cyclic steady state is given and the numerical results are compared with experimental measurements. The results show the need for identifying and evaluating economical means of removing the higher molecular-weight hydrocarbons and other highly adsorbed species from the gas stream before charging the storage reservoir.