Egged on by $100-a-barrel oil and consumers going green, venture capitalists plan to pour more cash into environmentally friendly technology this year, prompting talk of a bubble reminiscent of the dotcom era.

Some 61 per cent of 170 venture capitalists in one US survey said they believe the inflow of venture dollars into "cleantech" would overvalue the sector, even though many remain convinced of its long-term potential.

Too many dollars chasing too few deals - especially in areas most likely to catch the eye of investors - has led to overvaluations, said Rodrigo Prudencio, a partner at Nth Power, an energy technology venture capital firm.

"We're certainly seeing some evidence of overheating in the market where the dollars got invested in solar and biofuels," he said. "But it's too early to tell whether or not that creates something pandemic across the cleantech sector." Four out of five US venture capitalists expect cleantech to attract higher levels of venture funding this year compared with 2007, according to an annual survey by the National Venture Capital Association (NVCA), a trade group.

Last year, cleantech received $2.6 billion (€3.84 billion), or roughly one-tenth of all US venture money invested, a whopping 341 per cent increase from cleantech investments in 2000.

The upswing will continue this year amid hype around smart cars, green buildings and technologies that use the sun, wind, corn and water to generate power.

Pricier oil and growing worries about global warming have spurred the search for alternative technologies, analysts say.

Dan Pullman, a principal at boutique investment bank McNamee, Lawrence & Co, said greater consumer awareness and the absence of marketable, affordable clean technologies that people can employ in their own lives creates the long-term opportunity for VC funds. Currently, there are only about 42 US-listed companies making a cleantech product.

"We haven't all traded in our cars for Priuses yet," Mr Pullman said, referring to Toyota hybrid car.

Analysts likened venture investment in cleantech to the life sciences sector, because both have similar gestation periods and high failure rates. Life sciences, including biotechnology and medical devices, have a longer history in the VC world and get about one-third of venture dollars annually.