Ball bought his 1982 Mercedes 300D on e-Bay, and is so committed to the fuel that when his car arrived, he wasted no time.

"I drove it right off the boat and to Pacific Biodiesel and filled it up," he said.

Biodiesel, a fuel made from vegetable oil, is the latest thing in fuels — until ethanol gets mixed into gasoline in Hawai'i in 2006.

Singer Neil Young uses biodiesel in his cars when he's at his Big Island home. Country music icon and part-time Maui resident Willie Nelson fills up his Mercedes at the Pacific Biodiesel plant in Kahului; his wife fills up her diesel Jetta wagon there as well.

Singers Neil Young and Willie Nelson praise biodiesel fuel. Both are part-time Hawai'i residents who use biodiesel when in the Islands. National Biodiesel Board

"He's been our customer longest, for four or five years," said Pacific Biodiesel marketing director Kelly King.

Harrelson said he uses biodiesel to do his part "to help lessen the damage being done to the environment by fossil fuels."

"Because the Hawaiian Islands are so isolated, we have the unique opportunity and responsibility to be the model of sustainable living for the rest of the world," Harrelson said.

King said biodiesel requires no modification for use in diesel engines, and it burns cleaner, extends engine life and smells better, she said.

Ball said he always felt diesel cars smelled bad, but it never occurred to him that gasoline engines did.

King's husband, Robert King, started Pacific Biodiesel on Maui in 1996. The firm, still the only producer of the product in Hawai'i, gets used vegetable oil from restaurants and fast-food operations. It is filtered and chemically treated to remove glycerin and then can go right into diesel engines, either pure, or mixed with regular diesel fuel.

The company now has a Maui plant making about 200,000 gallons annually, and a plant on Sand Island that produces about 400,000 gallons a year. Most of the fuel goes into fleet truck and bus operations.

Because it burns cleaner than petroleum-based diesel, Maui Electric Co. uses biodiesel as fuel when the firm is starting up and shutting down 12.5-megawatt diesel generators at its Ma'alaea power plant.

"The engines when they're starting and stopping aren't as efficient as when they're running at normal load," said staff engineer Mark Ratte. He said that when starting up on biodiesel, they produce fewer visible emissions.

King said the firm's biggest customer on O'ahu is the City and County of Honolulu. In July, Maui County began using biodiesel, and some tour bus firms and tour boat companies also use it.

Hawaiian Electric's 120-truck diesel vehicle fleet on O'ahu uses it, "and it required no modification to either the trucks or our underground tanks," said spokesman Peter Rosegg.

Most of the fleets use what's called B-20, which is 80 percent standard diesel fuel and 20 percent biodiesel.

Maui County environmental coordinator Rob Parsons said biodiesel is a better lubricant than petroleum oils, and can make engines run more efficiently, longer. Even though the county pays about 14 cents a gallon more for a B-20 mix than for regular diesel, Parsons said there are other considerations.

"It's the right thing to do. It's available, and it's a local renewable," he said.

For the average driver, getting biodiesel isn't always convenient. Maui residents with diesel cars or tractors can buy B-20 at the Pa'ia Chevron station, where it recently was selling for $2.40 a gallon. Regular diesel was available from another service station for $2.79 a gallon.

Folks looking for the pure product can pump it at the Pacific Biodiesel plants at Sand Island, where it was recently selling for $2.49 a gallon — 5 cents cheaper than regular diesel — and at Kahului, where it was $2.59 a gallon.

Or you can do what Harrelson on Maui and Young on the Big Island do: install your own storage tank and have it shipped to you in bulk.

Another option is to rent a biodiesel car. Shaun Stenshol's BioBeetle has three cars on Maui and one on O'ahu that run fully on biodiesel.

"People just rave about it," Stenshol said. "My goal is to make Hawai'i environmentally sustainable."

King said that Pacific Biodiesel is using as much of Maui's waste vegetable oil as it can get, but still hopes to expand its supply on O'ahu.

"Some folks are still taking their waste oil and dumping it, which is bad for the environment, since it can seep into groundwater, and a waste," she said.

The company is discussing with Maui Land & Pineapple Co. the possibility of growing oil seed crops that would be harvested and converted into biodiesel fuel.

Nationally, most of the biodiesel is not made from waste oil but directly from virgin vegetable oils such as soy, said Jenna Higgins, of the National Biodiesel Board. Singers Nelson and Young use soy-based biodiesel when they're on the Mainland.