As gas prices continue to rise, the price gap is closing for environmentally friendly fuels like biodiesel.

This is making the fuel, a blend of traditional diesel and about 20 percent agricultural byproducts like vegetable oils or animal fats, more attractive for drivers.

"In this age, with the cost of traditional product rising so much, it's come time where it is economical to look at other sources," said Peter Russell of Santa Fuels.

Russell is getting more calls asking about biodiesel than he did in the past.

The company has been selling to commercial customers in New Haven, Connecticut for four years.

"The number one concern with most end users is cost. I think you get a lot of tire-kickers that would like to be environmentally friendly, but cost is always going to be the number one concern," Russell said.

Major universities including Yale University were early adopters of bio-diesel.

The university uses biodiesel to fuel its fleet of buses.

People are asking Volkswagen salesmen including Mike Rivers about a new clean-burning diesel Jetta, which advertises that it gets 40 mpg on the highway.

"This actually will get much better gas mileage than (a) regular fuel car," Rivers said. The old diesel VW engines have always gotten gas mileage in the 40s to low 50s, he said.

Some cars take only diesel because of the filter system but, in some cases, cars can be modified to take bio-diesel.

This might change with more cars being able to accept biodiesel.

"Eventually, I think we're going to see it in all the products we sell because we just need to supplement demand on the foreign oil and this is a perfect way to do it," Rivers said.