It depends, if you count the installation-costs, too. If you just look on the consumption, it's cheaper than fuel car, but not neccessarily cheaper than a Diesel-car.

In Germany and Holland the LPG-price is much lower than for fuel, but the consumption is ca. 10-15% higher than using fuel. So a very economical Diesel-car can be cheaper in use.

Driving LPG costs ca.10% of the engine-power,too. And the burning-temperature is a bit higher, so it's not a good choice for cars which are known for overheat-problems.

Oh, must there be a sticker on it? In Germany you only can recognize LPG-cars by the little black cap of the filler-hole somewhere at the back of the car. And by the smell, when they are passing you.

For a long time it was forbidden to enter underground-parkings and ferry-boats with LPG-cars, but as I know it's not any more in Germany.

In 1996 I've used illegally the Eurotunnel from France to Britain - the K 70 of my friend had LPG. It was forbidden in that years.
And he had even two big tanks mounted. The guy wanted to save money for fuel. So we entererd the UK loaded with 200 liters LPG and 52 liters of fuel.

e.g.:
http://www.imcdb.org/vehicle_8491-Dodge-W-200-1977.html
(green sticker on the rear)

CNG is not common in Canada. The government in Ontario was really pushing it in the early 1990's though.

LPG is great! My dad got a system insaled on his Fairlane, and after the goverment cashback for installing, it only cost him $450ish. LPG is over half the price of unleaded fuel (gas you Americans call it) and is just as good perforance. Another good one is GNG (compressed natural gas), and I hear that is commen in Canada.

Yes, the fuel consumption is higher on E85 than on regular 95 octane. I think they say that the price for the customer will be about the same.

Yes, but I heard that E85 vehicles run a higher fuel consumption when burning Ethanol. Whither true or not I don’t know.

I know the Ford Expedition has been modified to run E85 Ethanol for the 2009 model year. It bears a "Flex Fuel" emblem on the liftgate. Supposedly it can run strait Gas/Petrol or any mix of both Gas or Ethanol or just strait Ethanol.

Several GM cars are E85 capable (though I can’t remember which ones)

I didn't know that. We do have some bigger vehicles that can run on ethanol E85.

MBSL65fan: not only in Europe. You can mount the LPG-system in all cars with fuel-engines.
So many of the big US-made SUV's and Pick-ups over here have LPG, too. In Germany the price of LPG is around half of the 95-octane fuel.
In the Netherlands LPG is very popular, you can get it at nearly every just middle-sized gas-station.

LPG stands for liquified petroleum gas.