The shares climbed 3.9 percent to $25.08 at the close in New York. Earlier the shares rose as much as 19 percent, the most intraday since Feb. 10.
Tests showed oil at its Cameia No. 2 well at least 135 meters (443 feet) deeper than Cameia No. 1, Houston-based Cobalt said in a statement today.
Cobalt is preparing for an additional test in August and plans to evaluate data to determine the potential of the new zone. The company has a 40 percent interest in the block. Other partners are Sonangol EP, Nazaki Oil & Gaz SA and Alper Oil Limitada.
“We have a lot of work yet to do before we fully understand the magnitude of the Cameia discovery, but we believe that we are off to a great start with two successful wells in the field, and in our Angolan pre-salt exploration program,” Joseph Bryant, Cobalt’s chairman and chief executive officer, said in the statement.
Cobalt today reported a net loss of $141 million, or 35 cents a share, during the second quarter, compared with a net loss of $19 million during the same quarter of 2011. The loss included a write-off of $99 million in expenses related to two unsuccessful exploratory wells in the Gulf of Mexico, the company said in a statement.
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