Propane is a fuel just like diesel fuel or gasoline. While we usually see propane used to run back yard barbecues propane powered vehicles are not science fiction. Propane is usually burned as a gas but it is shipped, stored, and sold in liquid form under pressure. You take great care in where you buy your gasoline from, and you should take just as much care where you purchase your propane as well.
Most propane consumed is done so in the canisters you see attached to barbecues and the like. These canisters are typically swapped out in a cage and a full, new cylinder is paid for. For the consumer and retailer the value here is convenience. For the propane supplier the added bonus is they fill the returned tanks to their full capacity starting at whatever level the cylinder came to them. So, if a cylinder had a quarter of the propane left that means the consumer paid for a full cylinder but the supplier only has to fill it three quarters. The supplier makes more money in this case.
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