HOUSTON - In the next decade or so, some of that familiar smell of jet-exhaust fumes, detectable around airports when planes are taking off, may be replaced with the aroma of pond scum and suntan lotion.

OK, that may be a bit of an exaggeration. Actually, you probably won't be able to tell - or smell - that airlines increasingly expect to be powering their jets with biofuels made from plants and other organisms, including algae and coconuts.

Last week, Continental Airlines Inc. became the latest carrier to conduct a test flight of one of its planes, a 737 with one engine running on a blend of conventional jet fuel and a biofuels blend made from algae and the jatropha plant. Continental's two-hour flight from its Intercontinental Airport base here carried only two pilots and a flight engineer and was the first for a two-engine plane.

Continental joined a select club that includes Virgin Atlantic Airways Ltd. and Air New Zealand Ltd., which last year pumped biofuel blends into one of the four engines of 747 jets and took them out for a spin. Japan Airlines Corp. and JetBlue Airways Corp. are planning similar tests in coming months.

Virgin Atlantic used a mixture of oil from palm and coconut trees while the New Zealanders used just jatropha oil, derived from a scrubby plant that grows wild in tropical regions of the world.

The experimental flights are part of a feverish effort by the airline industry to save money and reduce its carbon footprint. A big part of the endeavor is finding alternatives to the petroleum-based kerosene that now is the only fuel approved for use in jet engines.

Oil dipped below $40 a barrel Friday, but last summer it spiked at $145, wrecking airline balance sheets and forcing deep cuts in service. When prices were peaking, fuel made up as much as half of the operating costs of some airlines.

"We're the only transportation mode that doesn't now have an alternative fuel. We want one," said John Heimlich, senior vice president and chief economist for the Air Transport Association, as he waited with hundreds of other industry officials and reporters in a Continental hangar for the test flight to take off.

The development of affordable, commercially viable jet fuel using renewable resources could still be sidelined by the same concerns that surround ethanol as an additive or substitute for gasoline.

Will the demand for biofuel plants be so great that it takes large amounts of land out of agricultural production and requires so much conventional fuel and fertilizer to grow that it will not help reduce demand for oil? Jatropha, for one, has not been successfully grown in large quantities, according to some studies.

But airlines, joined by Boeing Co., jet-engine manufacturers, and chemical companies, say the biofuels they are testing are "second generation," meaning they are made from sustainable crops that do not waste more energy than they save. And research and development of aviation biofuels is further along than you might imagine, officials said.

Continental said its test flight was the first to use oil derived from algae, which can be grown rapidly in brackish water in a variety of climates.

The need for greater fuel efficiency "has driven the industry for decades," said Billy Glover, Boeing's managing director of environmental strategy. For biofuels, "we've been accelerating down the runway . . . and now we're about ready to lift off to the next stage," he said.

Continental chairman and chief executive officer Larry Kellner told the throng of observers here before the flight that the industry hopes that within three to five years airlines will have biofuels available to them. But, he said, it may take a decade for there to be enough commercial production for it to be used extensively.

"We see biofuels as a place we can make significant progress," Kellner said. "The challenge will be to produce it in an efficient way in the quantities we need."

Last week's flight followed many hours of running jet engines on the ground using biofuel and biofuel-kerosene mixtures. The experimental flight involved the type of tests done on new planes and aircraft engines, including adding or reducing power, shutting down and restarting one engine at a time, and doing both normal and abnormal flight maneuvers.

The hunt for jet-fuel alternatives is part of a range of industry initiatives to not only save money but also convince the world that airlines do not deserve their reputation as polluters and energy wasters.

The major airlines all have sections of their Web sites devoted to reports on what they are doing to conserve energy and help slow down global warming. To find the reports on the sites, you have to drill down several pages, looking in sections for corporate information or press releases.

The Air Transport Association, which represents most U.S. scheduled airlines, also has a large portion of its site, www.airlines.org, given over to environmental affairs.

Although I am as quick as anyone to criticize the airlines when they provide lousy service or gouge customers, this is one area that I will give them credit for trying to simultaneously help the world and their own bottom lines.