Since the beginning of the U.S. space program, it has been postulated that as manned missions became longer and crew size increased, the penalties of storing or routinely resupplying consumables would at some point become prohibitively costly. This paper reports on a study that was conducted to determine what missions would benefit from Controlled Ecological Life Support System (CELSS) technology. The study focused on manned missions selected from NASA planning forecasts covering the next half century. Comparison of various life support scenarios for the selected missions and characteristics of projected transportation systems provided data for cost evaluations. This approach identified missions that could benefit from a CELSS, showed the magnitude of potential cost savings, and indicated which system or combination of systems would apply. The paper outlines the analytical approach used in the evaluation, describes the missions and systems considered, and sets forth the benefits derived from CELSS when applicable.