good point. mine are owned outright since '72, i just show them original paperwork on refills. my supplier will probably be able to answer my question re private sales & ownership papersI wondered too but my guess is if you don't return leased tanks, you would be sued and ultimately buy them anyways, and they have records on who leases them. I mean I have my receipt from where I spent $1500 on tanks and the Smith torch kit.