Here in Alberta, Canada, propane is widely available and often less than half the price of gasoline. It is the fuel of choice for taxis and other high-use vehicles, also many motorhomes. I have not tried it in my Volvos but have used it in Ford vans for at least 15 years. It is an excellent fuel. The trick, and expense, is in having the engine optimised for propane: high compression, hardened valve seats, the right cam (RV grind is great in a V8), correct ignition timing curve. My 351 Windsor, in a camper van used for hauling a horse trailer, now makes noticeably MORE power than it did on gasoline and gets almost the same fuel economy. A previous 302 engine which I parted out after running 250,000 miles on propane (I wanted the propane heads) was sparkling clean inside with no cylinder wear. I know, that would be nothing for a Volvo!

Natural gas: those conversions are available here as well, and you can indeed buy the equipment to refuel your vehicle from your home gas line, avoiding road tax legally. Some city busses here run on it, and delivery vehicles. Range is much poorer than propane because the fuel is a compressed gas rather than a liquid.

The point is, this is normal everyday technology here and in Europe. It only seems exotic in the USA, apparently!

Merry Christmas to all.