Says one stockbroker about a rush to invest in "green" companies, particularly alternate energy suppliers.
High oil prices, climate change and insecure supplies have sparked an explosion of companies seeking money to develop ways to ease the looming energy crisis.
However, some fear backers of growth firms on London's junior exchange, the Alternative Investment Market (AIM), could lose their shirts.
"It has all the makings for a bubble," said Keith Woolcock, director at Westhall Capital, a London-based stockbroker. "It could take a while to pop because we are in the very early stage."
Like Google and Microsoft, a handful of tiny companies could grow into profitable global players, he added.
"There's going to be a lot of investors who get burned, there's going to be a lot of investors who are going to make an extremely large amount of money," Woolcock said.
Spotting a winner is hard in a sector that sees profit in anything from pig manure and trapped mine gas to the oil of the tropical jatropha tree and the humble plastic recycling box.
"There are a lot of pitfalls," said Craig Pennington, global energy portfolio manager at Schroders, the asset manager. "There are a lot of losing money opportunities. I would definitely urge caution."
Even companies with a good idea have no guarantee of success of beating established firms with big research budgets.
"You have to have some degree of confidence that you're backing the VHS of alternative energy and you're not backing the Betamax," Pennington said, referring to Sony's defeat in the 1980s battle for the home video market.
The real warning here of course is that a lot of this "renewable" power is incremental in nature. It is not the revolutionary change needed to seriously effect how electricity is generated. Financial experts are warning that if governments get behind nuclear power, many, if not most, of these ventures will fail or be marginal performers at best.
Its chief executive Cameron Davies said the risk of investing in growing companies in the green sector is outweighed the growth potential.
He played down talk of the next Google emerging from the sector as "far-fetched."
"The thought of a company coming along with a magic idea is pretty unlikely," he said. "It's more evolution than revolution."
With green issues high on the political agenda, smaller firms could attract more investment.
British Prime Minister Tony Blair said this month that it was an "absolute necessity" to confront climate change, while President Bush said in February that "America is addicted to oil."
The green sector may lose its admirers if politicians look to nuclear power or if oil prices fall.
"Long-term prospects are pretty compelling, but for mainstream investors it's too high-risk," said Mark Hinton, research analyst at the financial advisers Bestinvest.
Norwich Union, which has a "green" fund run by Morley Fund Management, said last month demand for cleaner fuels would rise, but investors should be cautious.
"(Smaller) companies have yet to be profitable and are exposed to uncertainty over government policy," said Dr Peter Michaelis, manager of the Norwich UK Ethical fund.