Don’t tell a jet pilot that jatropha is just a tropical weed.

WASHINGTON - Burned by the cost of jet fuel, the aviation industry is trying everything from algae to camelina and jatropha as alternatives, but specialists say that some of the new fuels, which include coal, might simply trade one set of problems for another.


Recently, Continental Airlines tested a fuel made from algae and jatropha, a tropical shrub with an oil-bearing seed, in a Boeing 737 jetliner, in a two-hour flight beginning and ending in Houston.


The flight was the first airline trial of algae, and, perhaps more important, the first use of biofuels in a twin-engine jet. Air New Zealand flew a four-engine Boeing 747 recently with one engine on a 50 percent biofuel mix, and Japan Airlines plans to do the same as part of a series of tests. Although jet fuel prices have dropped with crude oil, industry executives say they are determined to become less dependent on a single source of fuel in case prices rise again.


“It’s hard to plan a business, and buy expensive pieces of equipment that last for 20 or 30 years, when you have total uncertainty about the cost of your biggest expense,”said John P. Heimlich, chief economist of the Air Transport Association, the trade group of the major airlines.


At Pratt & Whitney, the engine manufacturer, Alan H. Epstein, vice president for technology and environment, said,“It’s the first time in the history of jet aviation that the world is seriously considering going to a totally new fuel.”


Continental’s algae comes from a Hawaiian company called Cyanotech, which raises it as a nutritional supplement.


One oil substitute is already used in large volumes. Sasol, the South African coal company, for years produced semi-synthetic jet fuel, half from petroleum and half from coal, and pumped it into airliners leaving Johannesburg. In April 2008, the British Ministry of Defense approved the use of 100 percent synfuel, clearing the way for many airlines to use it.


The fuel has some advantages over traditional jet fuel, including extremely low sulfur levels, but when production is considered, jet fuel from coal produces substantially more carbon dioxide than jet fuel from oil.


Using a process similar to Sasol’s, a refinery in Qatar, in the Persian Gulf, is making a jet fuel substitute from natural gas.


At the fuel maker UOP, Jennifer S. Holmgren, director of renewable energy and chemicals, said fuel made from jatropha had only about half as much carbon dioxide effect as fuel from petroleum. This is significant because the European Union is trying to bring the airlines into a carbon dioxide reduction system.


Environmental advocates strongly favor low-carbon fuels, but only if they do not compete with food production.


By MATTHEW L. WALD