More work but consider this. Compressed Natural Gas sells in Utah for around 65 cents per gallon. We have lots of natural gas here! Other states it runs around $1.50 depending on the taxes. Mileage with a CNG conversion is about the same as gasoline. Three serious considerations though: 1. CNG seems only to be easily available in the southern and western states. Otherwise may be hard to find. You won't get it on I-90!! 2. The conversion is expensive - about $10,000 to $12,000 BUT there are federal and state rebates that start at $4,000 and can go as high as $8,000. 3. Conversion involves installing several heavy CNG tanks which will eat up a lot of space. My own take is that this is a good option for a pick-up truck but probably not for any other kind of vehicle though a local guy converted his Ford Crown Victoria.
Lots of good links if you google "CNG conversion."
Randy Lieber is a local advocate. See his position paper here:
http://www.scribd.com/doc/2275855/Fu...d%20cng%20tank