What are the advantages and disadvantages of LPG?

I had a buddy that had one that he added LPG to back in the 70's. The exhaust stinks. The energy in LPG is not as dense as gasoline so the engine does not produce quite as much power. If you are trying to save energy, you shouldn't be hotrodding it anyhow. It is not as easy to fuel up an LPG vehicle as one that uses a fuel that is liquid at room temperature. The pressure in the tank can reach 100 psi when it is warm. Back then, gasoline was about $0.75 per gallon and LPG was about $0.20 per gallon. Gasoline is around $3.49 per gallon and the last LPG that I bought was $1.99 per gallon. I don't know that the price difference now would make LPG much cheaper than gasoline, at least in the US. I think diesel would be the way to go. My son recently bought a 1 ton quad cab dual wheeled pickup with a 454 cid engine. He swapped the ger for a 379 cid diesel engine. Most people claim that it will double the mileage and with gasoline at $3.49 vs $3.89 per gallon for diesel, it should save quite a bit. We do not have the truck built yet, but hopefully soon. We are also converting it from 2wd to 4wd and from automatic to manual transmission.