An evaluation of environmental control system reliability data for Air Force Minuteman Wing I is presented. The data submitted by American Air Filter Co., are found to be a fair estimate of mean time between failures (MTBF), although modifying factors were not always applied. The data supplied by Holladay and Westcott were found to be unrealistic, mainly because not all sources of data were considered. Recommendations for system upgrading are made by STL for future wings of the Minuteman Program. These recommendations include such things as over design allowances, redundancy, use of best equipment, complete failure reporting, and use of modifying factors for correct determination of MTBF.