A Microchannel Sabatier Reactor System (MSRS) consisting of cross connected arrays of isothermal or graded temperature reactors is proposed. The reactor array enables nearly complete single pass carbon dioxide reduction using the Sabatier reaction, allowing efficient recovery of oxygen from in situ carbon dioxide resources on Mars or other Near Earth Objects. Arrays of microchannel reactors with decreasing temperatures and increasing residence times can be optimized to maximize reaction kinetics and overcome thermodynamic limits (85% conversion at 400 C)of the Sabatier reaction resulting in 99% conversion of carbon dioxide and hydrogen to water and methane. Alternatively, monolithic graded temperature reactors can be developed that will optimize reaction kinetics with respect to the thermodynamic limitations of the Sabatier reaction in a compact and efficient design. The Phase I efforts will focus on design and construction of the microchannel reactors. The Phase II effort will build upon the feasibility demonstration resulting in the development of a prototype MSRS consisting of a microchannel reactor array and a graded temperature microreactor capable of 99% single-pass, carbon dioxide conversion to methane and water capable of processing 1 kg hr-1.