What company sells oxygen?

Excuse me, I'm curious about a rather unique business model. Could you possibly enlighten me on which company specializes in the sale of oxygen? I've heard of various entities providing industrial gases or medical equipment, but I'm specifically interested in knowing which company caters to the retail market for oxygen. Is there a specific brand or chain that offers this service? I'm assuming it would be for recreational use or perhaps for those with medical needs who require home oxygen therapy. I'd appreciate any insight you could provide on this matter.