That's disgusting.
As for mileage... It's a truck so I only get about 15 miles/gallon.
However, you can get CNG vehicles that get better mileage. There are alot of Honda Civics that have been converted to CNG.
There's more info on this site
www.cngutah.com I'm by no stretch an environmentalist, but this Ford truck is one of the greatest things I've ever done financially.
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I saw two Personages, whose brightness and glory defy all description, standing above me in the air. One of them spake unto me, calling me by name and said, pointing to the other— This is My Beloved Son. Hear Him! -- Joseph Smith History 1:17