That's expected to give the Luanda government a big boost for its drive to double production in the West African state from the current 1.8 million barrels per day to 3.5 million bpd by 2020.
Much of that crude will go to the United States, already a major buyer of West African oil, and Angolan production will challenge Nigeria's long-held supremacy in Africa. China imports 15 percent of its oil from Angola.
Luanda is expected to auction exploration rights to major international oil companies early in 2013 following Cobalt's deepwater strike.
The company, which is backed by Goldman-Sachs, estimates the Kwanza strike in the Atlantic Ocean contains 1.5 billion barrels of oil.
The geological strata there are believed to extend westward across the Atlantic to Brazil.
Angola's offshore blocks have shown geological similarities with the bountiful Santos and Campos basins off Brazil where major discoveries have been made in recent years.
British Petroleum, Statoil of Norway, Total of France, ConocoPhillips of the United States and Italy's Eni already have stakes in 11 exploration blocks in Angola's Kwanza and Benguela basins to drill the pre-salt deposits, a geological layer dating from the dinosaur era about 100 million years ago.
"The Cobalt discovery proved that what was a concept -- the comparison between the Kwanza Basin and Brazil -- has become a reality," says Didier Lluch, regional exploration manager for Spain's Repsol, which recently acquired Angolan blocks.
"The bounty of crude deep under the Angola seabed counts as one of the most tempting targets for international oil groups," the Financial Times reported July 2.
But before that boom gets properly under way, the international oil companies will have to face major technological difficulties in extracting the oil from its deepwater vaults -- Cobalt's well reached a depth of nearly 5 kilometers, or just over 3 miles -- as well as political perils ashore amid an emerging power struggle over who'll succeed longtime strongman Jose Eduardo dos Santos when he steps down later this year.
"Getting to the oil … involves feats of engineering and the ability to navigate a country consistently ranked as one of the world's most corrupt," the Financial Times observed.
But, the business daily noted, "As Angola seeks fresh investment to add to the tens of billions of dollars energy groups have spent to make it Africa's second-biggest crude producer, oil companies' appetite shows no sign of abating."
The favorite to take over from dos Santos, who has ruled the former Portuguese colony for 32 years, is Manuel Domingos Vicente, who ran the state-owned Sonangol oil company for 12 years until January, transforming it into a conglomerate "likened by some observers to be a sovereign wealth fund."
The oil companies are paying huge signature bonuses to secure exploration rights, most of which, many observers say, end up in the hands of top Angolan officials.
Statoil, for instance, is estimated to have paid $1 billion for its stake. BP recently disclosed it plans to spend $15 billion in Angola over the next decade.
"Graft poses a risk too," the FT noted. Angola was ranked 168th out of 186 countries in Transparency International's most recent corruption blacklist.
In April, the Financial Times reported Vicente and two senior Angolan generals had earlier concealed holdings in Cobalt's local partner.
Cobalt lawyer Michael Goldberg said the company was "more convinced than ever that Cobalt has not violated any U.S. or Angolan laws."
Vicente has denied any wrongdoing.
The FT reported he had "dismissed concerns that such groups might serve as fronts for officials seeking an illicit share of the oil bonanza, which would leave foreign groups at risk of violating anti-corruption laws at home."
Vicente "is seen as someone who's popular with the oil companies because he was effective and good to do business with," observed Dairmid O'Sullivan, a researcher with the Global Witness advocacy group.
"But Angola's economy and Angola's future prosperity is based on oil and their record for using that oil for the benefit of the people is terrible."