The liability issues (fire, health), as well as the cost of getting the o2 concentration significantly above the normal 21%, would probably deter a casino operator from using oxygen on the casino floor, even if there were some advantage -- which is doubtful. Medical grade (100%) oxygen can be purchased only with a doctor's prescription. The only kinds of oxygen you can buy without a prescription are airplane oxygen (for use at high altitude)... and the sometimes-flavored 95% oxygen mixtures available at "oxygen bars" (some of which are located in casinos).