Although the deal gives Galp more cash than the minimum 2 billion euros ($2.7 billion) it had sought to help finance its share of the oil field development costs, the price Sinopec Group is paying disappointed Galp investors, sending the Portuguese firm’s shares down more than 13 percent on Friday.

Galp had been expected to raise 2 billion euros from selling a stake of at least 20 percent.

The deal follows Sinopec’s $7 billion acquisition last year of a 40 percent stake in the Brazilian arm of Spanish oil company Repsol and a separate offshore oil development deal in April with Brazil’s state-controlled oil company Petrobras.

“For Sinopec, there are not many opportunities to grow in the traditional domestic upstream oil and gas sector — overseas acquisition is an area to find growth,” said UOB Kay Hian analyst Yan Shi.

“It will benefit Sinopec on upstream reserves, and reduce risks in its money-losing downstream operation.”

But Galp’s share price was down 13.4 percent at 12.86 euros by 1300 GMT in heavy turnover, topping the FTSEurofirst 300 decliners board.

“The implied values of Galp assets from that deal are disappointing. Repsol got $5.6-5.8 per barrel of reserves and this deal works out at $3.9 per barrel,” said Pedro Pintassilgo, fund manager at F&C in Lisbon.

The deal also knocked fellow Brazil-exposed oil and gas major BG Group, down more than 2 percent, while the Dow Jones Stoxx Europe Oil and Gas index was up 0.3 percent. Repsol, by contrast, was up 2 percent.

The head of Brazil’s Petrobras said last month BG may sell shares in its Brazilian subsidiary.

Santander analyst Jason Kenney said the Galp-Sinopec deal means Sinopec is “not paying up on the commercial valuation that we were all expecting to see.”

“If you can’t get the value for the assets in a commercial transaction then people do begin to question the value of the underlying asset base and so therefore the readacross for BG Group is negative.”

Galp said the deal valued its total existing assets in Brazil at $12.5 billion and that the operation “significantly strengthens Galp Energia’s capital structure, fully securing its funding needs for the future expansion and development of its upstream activities.”

Galp is a minority partner with Petrobras in key finds including the vast Lula field, formerly known as Tupi, where BG is also a partner, as well as the Cernambi and Iara finds.

Buyouts such as the Sinopec-Galp deal are on the rise because Brazil halted auctions for deepwater blocks to revamp its oil laws. Further bidding rounds for exploration leases are currently stalled by a dispute among states over how to divvy up royalties.

Chinese companies have invested in Brazilian industries ranging from iron ore mining to soybean cultivation, helping lift commodities production. But trade tensions have risen in recent years as Brazilian manufacturers complain they are being undercut by imports from the world’s second-largest economy.

Brazil’s vast deepwater subsalt oil deposits, located in an area the size of New York state believed to hold 50 billion barrels of oil, have drawn in the interest of oil giants such as Exxon and Shell.

Under the development plans Sinopec expects to get 21,300 barrels of oil equivalent per day (boedp) in 2015 with production expected to peak at 112,500 boedp in 2024.

Under the agreement, Sinopec’s wholly owned unit, Sinopec International Exploration and Production Corp. (SIPC), will take new shares to be issued by Galp and assume shareholder loans, Sinopec Group said in a statement.

“Taking into consideration this investment and projected future capital expenditure, the total cash payout amounts to approximately $5.18 billion at closing,” Sinopec said.

The transaction must be approved by the Chinese government.

China’s outbound acquisition deals this year totalled $37.6 billion, down from $54.1 billion last year, according to Thomson Reuters data.

Sinopec Group is the parent of Hong Kong-listed and Shanghai-listed China Petroleum & Chemical Corp. (Sinopec) . The group does overseas upstream oil and gas investment and operations via its wholly owned unit SIPC.

Sinopec was advised by Societe Generale, while Galp Energia was advised by Bank of America Corp, J.P. Morgan , UBS Caixia BI, a source familiar with the matter said.