RIO DE JANEIRO—The world’s largest energy companies line up Thursday for a major auction of coveted Brazilian oil fields, even as Brazil’s government rolled back some market-friendly policies that would have made its oil industry more competitive.
Exxon Mobil Corp. , Chevron Corp. , China’s Cnooc Ltd. and Spain’s Repsol SA are among 16 companies cleared to bid on four blocks in the Campos and Santos basins, thought to hold some 14 billion barrels of oil.
It is the government’s fourth auction of areas in the pre-salt region of southeastern Brazil where as much as 100 billion barrels of crude are believed to be locked under salt layers far beneath the seabed.
The pre-salt reserves were discovered in 2006, but private companies were kept away and production delayed by rules that required state-controlled Petróleo Brasileiro SA, or Petrobras, to be the operating partner with at least a 30% stake in any consortium in the region.
The government eased those rules last year to allow other companies to work without Petrobras if the state giant declined to participate in a project, although Petrobras still has the option to be the operator in areas it chooses.
The auction comes just days after Brazilian truckers went on strike to protest diesel prices that have soared along with international oil prices. The strike brought commerce to a standstill, and forced the government to reinstate price controls for diesel using tax cuts and other subsidies which it estimated will cost $2.5 billion this year.
The decision prompted the resignation of Petrobras’ market-friendly chief executive Pedro Parente, who had relied on the market pricing policy of the past two years to improve results and lower debt at the state oil company.
Despite wavering over fuel prices, the government has a history of respecting contracts in the oil industry, leading analysts to believe companies securing blocks in the pre-salt would avoid any potential backpedaling in the future.
Thursday’s contracts will be awarded to those that offer the biggest share of future production to the Brazilian government. Industry officials say bids could run as high as 75% of oil produced, a level first seen in an auction of pre-salt blocks in September.
The government also expects to collect around $800 million in signing fees.
“High interest for the pre-salt is leading to very risky bets,” said Juliana Miguez of Wood Mackenzie energy consulting group. She warned projects could become unprofitable if production doesn’t turn out as expected, “but based on pre-salt estimates, they are feasible.”
The long-term nature of the projects is also making bidders play down near-term concerns, analysts say.
“The exploration cycle can last two governments,” or eight years, said Helder Queiroz Pinto Junior, an economics professor and former oil regulator. “The companies focus on the geological conditions, and these are promising areas.”
Petrobras has said it is interested in being the operator in three of the areas, a sign for some that the blocks hold good prospects.
“No one knows the Brazilian coast better than Petrobras,” said Adriano Pires, director of Rio-based think tank Brazilian Infrastructure Center. “Investors recognize that the company…has been very careful in its investments decisions.”
Write to Luciana Magalhães at Luciana.Magalhaes@wsj.com and Paulo Trevisani at paulo.trevisani@wsj.com