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Shares of Sinopec jumped more than 3 percent in early Hong Kong trade in reaction to the plan announced on Sunday, outperforming a 0.7 percent gain in the blue-chip Hang Seng Index.
"The announcement... is the first step toward restructuring the business toward the upstream which is likely to see a gradual improvement in returns and potentially significant value upside in the long term," Scott Darling, head of Asia oil and gas research at Barclays Capital, wrote in a note.
Sinopec Corp has lagged behind bigger domestic energy producer PetroChina Co Ltd in acquiring overseas fields to offset refining losses, having made its first and so far only purchase of upstream assets in 2010.
Chinese refiners cannot fully pass on higher crude oil costs to customers because of government price controls.
Sinopec Corp said a year ago that it was considering buying more overseas upstream assets from its parent Sinopec Group to boost oil and gas production and counter losses.
Sinopec Corp - which relies on imports for most of the crude it refines - said late on Sunday it would set up a joint venture with its parent that will acquire $3 billion worth of oil and gas assets held by the latter.
The deal would boost Sinopec's proven reserves by 9.1 percent to 3.1 billion barrels of oil equivalent (boe), and its annual crude production would rise 11.2 percent to 365 million barrels, the company said.
The 50/50 venture will buy oil and gas-producing assets with 310 million barrels in proven and probable reserves from Sinopec Group, formally known as China Petrochemical Corp.
Sinopec Corp, whose oil and gas output reached 427.95 million barrels in 2012, will use internal funds and loans for its share of the venture. It said it would take management control.
Parent's assets
Sinopec Group has spent around $40 billion buying global assets in the last three years, including the $7.24 billion purchase of Swiss explorer Addax Petroleum Corp in 2009 to gain access to fields in West Africa and Iraq's autonomous Kurdistan region.
At least half of the group's overseas assets are in countries such as Syria, Argentina and Russia, where the reserves are either of poorer quality, too small or in areas fraught with political risk, analysts say.
Sinopec Group may eventually inject as much as half of its global oil and gas reserves into Sinopec Corp, which is far from enough to cut the unit's exposure to unprofitable refining at home.
The assets Sinopec Corp is buying through the joint venture were located in Kazakhstan, Colombia and Russia.
The venture will buy 50 percent of issued share capital of Caspian Resources Ltd in Kazakhstan for $1.6 billion, and 50 percent of Mansarovar in Colombia for $428 million that includes the takeover of a loan of $348 million from Mansarovar's shareholders, it said.
Sinopec will also buy from its parent 49 percent of issued share capital of Taihu - a partnership with Russian oil giant Rosneft in Russia - for $560 million and a special dividend held by its parent in the partnership for $93 million.
Sinopec, which on Sunday reported a 12.8 percent fall in 2012 net profit due to a drop in revenues from its upstream and chemicals businesses, bought deepwater oilfields in Angola from its parent for $2.46 billion in 2010.
Its refining division - where throughput edged up 1.8 percent to 221.31 million tonnes last year - made an operating loss of 11.95 billion yuan under Chinese accounting standards, compared with a loss of 37.6 billion yuan the previous year.
