Is Craig Venter going to save the planet? Or is this more hype from one of America’s most controversial scientists?

In a pristine white greenhouse in La Jolla, Calif., maverick molecular biologist Craig Venter is showing off tubs of dark green goop that might help rescue the planet.

Winter sunlight streams through the glass roof onto rows of long, white troughs filled with algae and seawater. A little water wheel in each trough turns to keep the liquid circulating and the growing cells evenly exposed to light and to carbon dioxide-enriched air. Computers maintain a constant temperature. Giant transparent bags of algae varieties waiting to be tested hang from metal beams.

This goop, Venter hopes, will someday replace oil wells, free the planet from its dependency on fossil fuels and create a near-endless supply of energy.

Jim Flatt and Paul Roessler, two senior scientists at Venter’s company, are leading guests through the greenhouse and trying not to reveal too many details about their ambitious venture. But their hypercompetitive boss, who has made a career out of shaking up the cautious culture of science — sometimes prematurely, critics say — keeps chiming in.

The strategy, Roessler explains, will be to grow oil-producing algae in concentrated conditions, “to maximize photosynthetic productivity and take up greenhouse gases at the same time.” Venter jumps in: “This is our halfway house ... a long way from the lab. The next phase is doing this in large outdoor facilities.”

How large?

Gigantic, Venter says. “We’re thinking a facility extending over multiple square miles.”

Venter and the scientists at his six-year-old company, Synthetic Genomics, are seeking strains of algae that are exceptionally good at turning carbon dioxide, water and sunlight into oil. The researchers intend to use genes from those strains to engineer algae cells that are even better at pumping out oil. Eventually, ExxonMobil, which plans to spend $600 million, $300 million of that in collaboration with Synthetic Genomics, hopes to refine oil from algae into gasoline. Other oil companies are joining biotech firms in similar efforts; Venter’s main competition may come from researchers trying to reengineer yeast or bacteria to ferment sugar into hydrocarbon fuel.

Last year, Venter’s Rockville-based J. Craig Venter Institute (JCVI) generated headlines when it said its scientists had made what they called “synthetic cells.” The announcement received plaudits from scientists, evoked alarm among some environmental groups, and prompted President Obama to ask his bioethics commission to assess the benefits and risks of the new field of synthetic biology. Although some critics called the development little more than an impressive engineering feat, Venter predicts that creating relatively simple, lab-designed cells, rather than tinkering with the genes of existing bacterial species, will become the future of biotechnology.

Back in 1998, J. Craig Venter — a former National Institutes of Health researcher — ignited a bitterly fought race to decode the human genome when he boasted that his company would beat the publicly funded, international Human Genome Project by finishing the job within three years. He even suggested that his rivals could best help out by abandoning their work on human genes and focusing on the genome of the mouse.