Exxon Mobil Corp. (XOM)’s $600 million foray into creating motor fuels from algae may not succeed for at least another 25 years because of technical hurdles, said Chairman and Chief Executive Officer Rex Tillerson.

So far, scientists haven’t been able to develop a strain of algae that reproduces quickly enough and behaves in a manner that would produce enough raw material to supply a refinery, Tillerson said in an interview taped for “Charlie Rose” on the PBS television network.

“We’ve come to understand some limits of that technology, or limits as we understand it today, which doesn’t mean it’s limited forever,” Tillerson said, according to a transcript of the interview. The venture is “probably further” than 25 years away from successfully developing fuels.

Exxon, the world’s biggest maker of gasoline and diesel, has been studying the potential for algae-based fuels for 3 1/2 years in a joint venture with J. Craig Venter’s Synthetic Genomics Inc. When the project was announced in July 2009, Exxon predicted it could produce fuels in five to 10 years.

When the venture was announced, the companies said they would build a greenhouse near San Diego to test various algae strains. The goal was “to produce a new source of oil,” Emil Jacobs, Exxon’s vice president of research, said during a July 14, 2009, conference call.

Venter, best known for his role in the sequencing of the human genome in the 1990s and early 2000s, said during the same call that algae ponds would produce 10 times as much fuel as the ethanol fed by corn fields covering the same amount of space.

“What we’ve come to understand is the hurdle is pretty high and the hurdle seems to exist at the basic science level, which means it’s even more difficult to solve,” Tillerson said. “These are very challenging problems.”