A comparison of the effects on recovery while breathing a 97 per cent oxygen mixture and normal compressed atmospheric air after treadmill running was determined among nine male wrestlers at Utah State University. The variables examined were heart rate and percentages of oxygen and carbon dioxide in expired air. The practice of some athletic teams of administering oxygen to participants during time out periods was the motivation for this study. A great majority of the studies reviewed conclude that oxygen does not play a significant role in aiding recovery from physical activity. The experiment first consisted of eight runs on the treadmill (Quinton Model 18-49-C) to familiarize the subjects with the equipment and also to enable them to plateau in conditioning for a five minute run at 0 per cent grade at eight miles per hour. After the training period was completed, the nine subjects went through a series of six runs, each followed immediately by a five minute recovery period while breathing a 97 per cent oxygen mixture for three of the recovery periods, and a 21 per cent oxygen mixture for the other three recovery periods. Heart rate was recorded every 30 seconds during the recovery period by the use of three electrodes on the subjects. Expired air was collected with the use of the Kofrany-Michaelis Respirometer. Air samples were analyzed for percentages of oxygen and carbon dioxide by the Fry Gas Analyzer. An analysis of variance showed no significant difference in heart rate decline while breathing either gas mixture. At the end of the five minutes of recovery, the subjects expired 3 per cent of carbon dioxide regardless of which oxygen mixture was breathed. It was concluded that there were no significant differences in the effects on recovery while breathing the 97 per cent oxygen mixture or the 21 per cent oxygen mixture.