GreenFuel Technologies (Cambridge, Massachusetts), one of the first companies to enter the algal biofuel industry, folded in May—a sign that investors may be starting to weed out the weaker players. GreenFuel raised at least $33 million from investors between 2005 and 2008, but in recent months couldn't garner another round of funding. GreenFuel claimed it was a victim of the economy, but some algae researchers say the company's technology simply wasn't economical, and investors had wised up. “It was a crappy business plan,” says Stephen Mayfield, a biologist at The Scripps Research Institute in La Jolla and an advisor to Sapphire Energy, an algae company in San Diego. GreenFuel's plan was to grow algae in photobioreactors fed with carbon dioxide from industrial emissions, and produce oil for fuel and other products. But the photobioreactors proved to be twice as expensive as calculated (Nat. Biotechnol. 27, 15–18, 2009) and oil yields fell far short of the quantities GreenFuel had expected. “My bet is investors finally got around to doing the numbers,” says Mayfield. GreenFuel's demise may be a sign that the field is maturing. More than 100 algae companies have popped up in the last five years. “In the next year we'll see lots and lots of these companies start to fold,” says Mayfield.