Cars that run on LP Gas (or LPG or Liquefied Petroleum Gas)

I read from some online mags that LPG costs 1/2 of that of octane 95 unleaded fuel. And that cars overseas have been modified to run on dual fuel systems.

Here are some pics:

This is the steel container for LPG situated in the trunk of a Hyundai XG dual fuel vehicle :-
[Broken External Image]:http://twnext.atnext.com/images/next-photos/TaiwanNext/216/640pixfolder/092-096-A216TEC10/d-2no.jpg

You can see the intake nozzle for LPG (red circle) :-
[Broken External Image]:http://twnext.atnext.com/images/next-photos/TaiwanNext/216/640pixfolder/092-096-A216TEC10/d-4.jpg

A meter shows what sort of fuel the car is running on. The red LED indicates that it is running on regular petroleum :-
[Broken External Image]:http://twnext.atnext.com/images/next-photos/TaiwanNext/216/640pixfolder/092-096-A216TEC10/d-3no.jpg

Then I found this link that elaborates more on LPG, I wonder if this is of any significance? I don't recall you guys & gals mentioned this before? Or is it called something else in the US?

>> World LP Gas Association