As recently as two years ago, few energy analysts believed that ocean power harvesting electricity from tides and waves had a future. Offshore conditions seemed too harsh, the costs too high. The International Energy Agency, a Paris-based research body that advises western governments, dismissed the technology in one paragraph in a 570-page study of energy resources that it published in 2004, saying it was "still in its infancy." But with crude oil heading to $80 a barrel, interest from both investors and researchers has surged.

"We've studied the sector and determined it would be an attractive sector in which to invest," said Charles Vaslet, an analyst at SAM Private Equity in Zurich. SAM has helped to finance two pioneer wave energy businesses, Ocean Power Delivery, a Scottish company based in Edinburgh that builds deep sea wave generators, and Energetech Australia, a company in Sydney that generates power from near-shore devices. Large financial companies like Merrill Lynch, utilities like RWE of Germany and turbine makers like the German engineering conglomerate Siemens, and General Electric, are also getting involved.

The money being invested in renewable energy sources, including ocean water, "is growing at an unbelievable clip, " Jonathan Shrader, a spokesman at the U.S. Department of Energy, said.

The IEA, too is paying fresh attention. While still cautious on environmental grounds and skeptical of the short-term potential, agency reports this year have played up the medium and long-term potential.

"The oceans contain a huge amount of power," said an IEA report on renewable energy development in February. "The resource is theoretically much greater than world energy demand."

Early interest focused on tidal systems, like the Rance estuary dam built by Electricite de France in Brittany in the 1960s.

Tides behave predictably. "You're guaranteed to have them twice a day and you know how strong they're going to be," said a spokesman at the Department of Trade and Industry in Britain, where a small experimental tide power generator was installed off Lynmouth, in Devon, in 2003.

But the cost, and the environmental impact of massive dam projects, has swung current interest more toward wave generation.

Among recent deals, a consortium led by the Portuguese utility Enersis last year signed an 8.2 million, or $10.5 million, order to buy three machines from Ocean Power Delivery, which are expected to start operating later this year, Max Carcas, Ocean Power's business development director, said.

The machines, semi-submerged, snake-like articulated cylinders, use internal hydraulic pistons to convert wave motion to electricity.

The consortium has signed a letter of intent to buy another 28 machines that would make the project big enough to power 15,000 households, while cutting unit costs, Carcas said.

"With wind turbines, you've seen costs decline by perhaps a factor of five. We see similar potential for wave energy, if not greater," he said.

Jan Bunger, research and development coordinator at the Danish Energy Authority, said costs could fall even further if power from sea water is produced at offshore wind energy farms like those installed off Denmark. "We are looking at options for combining the two technologies. We have some space between the wind turbines and we can use it to put in wave power turbines," he said.

Some of the costs reflect the need for the equipment to withstand harsh offshore conditions, including powerful storms. "It's technology that's for the big guys," noted Bunger. "We had kind of a bottom-up development with wind energy because every farmer could buy a wind turbine," but ocean energy "requires economic power."