British Petroleum is a good investment now, says Texas billionaire energy investor T. Boone Pickens as the company rebounds after losing more than half its value following the Gulf of Mexico oil spill.

“They will further damage their image when they start the investigation, but today BP is good buy,”  Pickens, chairman of Dallas-based BP Capital LLC, told Bloomberg.

Regulatory filings show that Pickens’s investment fund held no shares in BP as of the end of March, but did have a position in Transocean, which leased to BP the Deepwater Horizon rig that exploded several months ago, in Anadarko Petroleum, which is a partner in this well, and in the Halliburton Co., which contracted to work on the well.

“We still have the Transocean, I think we added to them,” Pickens says.

BP shares rose about 8 percent and other energy stocks rallied late Thursday as the British oil giant said it succeeded in stopping the flow of oil into the Gulf of Mexico for the first time since April.

Shares rose $2.74, or 7.6 percent, to close at $38.92 Thursday, They were up about 3 percent as BP began testing a cap atop the gushing oil well. The shares shot higher in the last hour of trading after BP announced the oil had been stopped when all valves on the cap were shut, as part of the test, the Associated Press reported.

Meanwhile, Dow Jones Newswires reports that BP’s North American biofuels business has agreed to buy Verenium Corp.’s cellulosic biofuels business for $98.3 million.

Under the agreement, Verenium will retain its commercial enzyme business, including its biofuels enzymes products, as well as certain reseach-and-development capabilities and access to some biofuels technology that BP may develop using what it is acquiring from Vernium.