BUENOS AIRES — Off the coast of Rio de Janeiro — below a mile of water and two miles of shifting rock, sand and salt — is an ultradeep sea of oil that could turn Brazil into the world's fourth-largest oil producer, behind Russia, Saudi Arabia and the United States.
The country's state-controlled oil company, Petrobras, expects to pump 4.9 million barrels a day from the country's oil fields by 2020, with 40 percent of that coming from the seabed. One and a half million barrels will be bound for export markets.
The United States wants it, but China is getting it.
Less than a month after President Obama visited Brazil in March to make a pitch for oil, Brazilian President Dilma Rousseff was off to Beijing to sign oil contracts with two huge state-owned Chinese companies.
The deals are part of a growing oil relationship between the two countries that, thanks to a series of billion-dollar agreements, is giving China greater influence over Brazil's oil frontier.
Chinese oil companies are pushing to meet mandatory expansion targets by inking deals across Africa and Latin America, but they are especially interested in Brazil.
"With the Lula and Carioca discoveries alone, Brazil added a possible 38 billion barrels of estimated recoverable oil," said Luis Giusti, a former president of Venezuela's state oil company, PDVSA, referring to the new Brazilian oil fields.
"That immediately changed the picture," he said, adding that Brazil is on track to become "an oil giant."
During Mrs. Rousseff's visit to China, Brazil's Petrobras signed a technology cooperation deal with the China Petroleum & Chemical Corp., or Sinopec.
Petrobras also signed a memorandum of understanding with Sinochem, a massive state-owned company with interests in energy, real estate and agrichemicals.
The Sinochem deal aims to identify and build "business opportunities in the fields of exploration and production, oil commercialization and mature oil-field recovery," according to Petrobras.
The relationship with China goes back to at least two years before Mr. Obama came to Brazil to applaud the oil discovery and tell Mrs. Rouseff:
"We want to work with you. We want to help with technology and support to develop these oil reserves safely, and, when you're ready to start selling, we want to be one of your best customers."
China rescued Petrobras in 2009, when the oil company was looking at tight credit markets to finance a record-setting $224 billion investment plan. China's national development bank offered a $10 billion loan on the condition that Petrobras ship oil to China for 10 years.
A chunk of Brazil's oil real estate appeared on China's portfolio in 2010, when Sinopec agreed to pay $7.1 billion for 40 percent of Repsol-YPF of Brazil, which has stakes in the now internationally famous Santos Basin, and the Sapinhoa field, which has an estimated recoverable volume of 2.1 billion barrels. Statoil of Norway also agreed that year to sell 40 percent of the offshore Peregrino field to Sinochem.
Last year, Sinopec announced it would buy 30 percent of GALP of Brazil, a Portuguese company, for $3.5 billion. GALP has interests in the Santos Basin and a 10 percent stake in the massive Lula field.
"The $5.2 billion cash-in we will get from Sinopec is paramount for our strategy in Brazil," GALP CEO Manuel Ferreira de Oliveira told Bloomberg News.
"It will give us a rock-solid capital base as we enter a decisive investment period at the Santos Basin. This operation values our existing Brazilian assets at $12.5 billion and is really a landmark for the company and for our shareholders."
News reports in December said Sinopec is the current favorite to buy stakes in Brazilian oil owned by Britain's BG Group, which also has interests in the massive fields of Carioca, Guara, Lula and Lara.
On Jan 8., the French company Perenco announced it was selling Sinochem a 10 percent stake in five offshore blocks located in the Espirito Santos Basin. Some of the transactions still await approval by Brazil's government.
In December, Venezuelan Oil Minister Rafael Ramirez publicly reiterated his government's commitment to an oil refinery joint venture with Petrobras.
That project reportedly is set to be funded by China's national development bank. Some news reports have quoted the head of China's development bank saying that new deals with Brazil are under consideration.
James Williams, an energy economist with the U.S. consulting group WTRG Economics, said the Chinese are taking on big risks with ultra-deep-water investments.
"But for them, the benefits are greater, as they become partners with companies that have better technology and expertise," he said.
• This article is based in part on wire service reports.