Oxygen enrichment of room air has proved to be valuable for people who need to work at altitudes of 4000 m and above. In the present study the feasibility of using the same technique in ski and other mountain resorts at the lower altitudes of 2500 to 4000 m is considered. Although many people find these altitudes invigorating, some are distressed by the hypoxia, especially at night. The analysis shows that all resorts up to an altitude of 3250 m (10,600 ft) can have the equivalent altitude reduced to 1000 m (3280 ft) by oxygen enrichment without incurring a fire hazard. (The equivalent altitude is that which provides the same inspired P(O2) during air breathing.) Even resorts or laboratories as high as 4250 m can have the equivalent altitude safely reduced to 1500 m, that is, lower than the altitude of Denver, Colorado. This application of oxygen enrichment is likely to be most valuable for improving sleep and assisting in the initial acclimatization process.