Propane prices vary widely, much more than gasoline, at least here in the U.S. Availability can also be an issue. Most newer gasoline engines will run fine as a properly converted dual fuel engine. The octane rating for propane is considerably higher than gasoline but the energy content per gallon is less. Some U.S. states give a break on annual registration fees (Arizona for one) if dual fuel equipped.
Back in the 80's when propane was more popular, it was usually considerably cheaper for the non-fleet user as far as BTU/$/Gal goes. Now it's a **** shoot depending on where you are and the price spread between propane/gasoline. You can find online conversion apps to determine if the price spread makes sense in your area. Everything considered, it's usually not which is why propane has fallen out of use in the U.S. as far as a vehicle fuel. Propane does give you another fuel option though if gasoline becomes unavailable for any reason.
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