Auto gas is propane, it's just that the garage stores it in large quantities and you put it in a converted car just like petrol. Exept it's under pressure and it's a liquid.
Forklift trucks and indoor plant runs of autogas, it's in red bottles there's an arrow painted on the bottle (when it's on it's side) that always has to point down, thats beacuse the liquid draw of tube is in that position. If wrongly mounted IE with the arrow horizontal then when the liquid level falls below the arrow head the engine will stop as it can't run on vapour IE gas it must draw liquid, or at least have the liquid forced out under pressure.
You can get propane bottles that stand vertically, they have a special valve with a long tube to the bottom of the bottle so as to get liquid and not gas. Some small engines however can operate on the vapour/gas off a standard propane bottle
Autogas at petrol stations is LPG (liquifed petrolium gas) it's "liquified" by compressing it hence it's stored at high pressure. When the high pressure si released it vapourises into a gas, thats why you get ice round filling nozzles and on the bottles when gas is being used quickly