An oxygen cart comprises a post connected to a handle and a bracket, a plurality of wheels connected to an underside of the bracket, at least one tank holder connected to an upper side of the bracket for holding portable gas tanks, and a tank support wall connected to and extending up from the tank holder said tank support wall keeping a gas tank in the holder when the cart is moving. There is a cart support surface connected to a lower end of the tank support wall for stabilizing the cart in an upright position when the cart is not moving. In order to accommodate several sizes of tanks, the tank holder has an upper section and a lower section, the upper section having diameter larger than the lower section, such that the upper section accommodates one size gas tank, and the lower section accommodates a different, smaller size gas tank. To accommodate an even smaller tank, a ring having an inner circumference that is smaller than a circumference of the lower section is used. The ring is placed inside the lower section allows the lower section to accommodate a gas tank having a circumference equal to or smaller than the inner circumference of the ring.