Side fill liquid oxygen vessel: A liquid oxygen vessel comes with a stroller/carry set/portable oxygen unit. The stroller/carry set/portable unit can be filled depending the type of vessel provided on the side or on the top of that base vessel. The side fill models are easier and safer as the connection valves don't get the possibility to freeze. Depending the country one would require the medical liquid oxygen one could be provided with either one of these systems. The side fill is generally the newest but most oxygen users are used to the top fill.