* CNPC, Petronas working with advisors to place bids
* Marathon plans to exit entire 10 pct stake in two fields
* Asia share of global oil and gas deals more than doubles in past decade
* Global oil and gas M&A hit a record in 2012
By Denny Thomas and Saeed Azhar
HONG KONG/SINGAPORE, April 3 (Reuters) - China National Petroleum Corp and Malaysia's Petronas are considering bids for Marathon Oil Corp's stakes in two Angolan offshore oil and gas fields, people familiar with the matter said.
This would be potentially the third major energy deal in Africa this year, a major new front for Asian state energy firms looking to fuel fast growing economies.
Reuters estimates that at least $6 billion worth of oil and gas blocks are being sold by U.S. independent companies, under pressure from shareholders and taking advantage of Asian interest to sell out of non-core assets. In total about $16 billion of oil and gas blocks are being sold globally, with $11 billion of that in Africa.
It also signals another banner year for oil and gas M&A, after a record $345.9 billion last year. Asian firms' share has more than doubled in a decade, according to Thomson Reuters data, to 19.6 percent in 2012 from 7.6 percent in 2003.
Sanjeev Gupta, an Ernst & Young partner and co-author of a report on oil and gas M&A, told Reuters affordability is not an issue for these large state companies because they have access to cheap government-backed funding.
"The Asian national oil companies are expected to pursue overseas acquisition opportunities despite substantial economic worries and geopolitical uncertainty," said Gupta.
CNPC, China's largest oil and gas company by production and the parent of listed company PetroChina Co Ltd, last month agreed to buy a $4.2 billion stake in a Mozambique offshore natural gas field. U.S. oil explorer Anadarko has also put up a stake in a Mozambique field that could fetch $4.5 billion.
Petroliam Nasional Bhd, Malaysia's state oil company, has also been stepping up its overseas purchases. Last year, it paid C$5.2 billion ($5.1 billion) to buy Canada's Progress Energy Resources Corp.
Houston-based Marathon first laid out plans in late 2011 to divest up to $3 billion worth of assets to plough money back into other operations.
Marathon has put its entire 10 percent stake each in Blocks 31 and 32 offshore Angola up for sale, the people said. The two Asian energy companies are working with advisors to place bids, though no deal was imminent, they added.
BP, Total SA and Angolan state energy company Sonangol are among Marathon's partners.
Marathon, CNPC and Petronas declined to comment. Sources declined to be identified as the sale process is confidential.
Marathon's sale of Angolan blocks is tricky as Sonangol has the first right of refusal on the blocks. In 2009, Sonangol blocked a $1.3 billion deal to sell a 20 percent interest in the 32 block to China's CNOOC and Sinopec by exercising this right.
Marathon had already sold its Alaskan assets last month and its production levels in Libya remain uncertain following the conflict in the region. It also has operations in Canada, Norway, Poland and Indonesia.
Marathon's Angolan sale comes as other U.S. independent oil majors are preparing for asset sales.
Hess Corp, which has been besieged by activist investors pushing for change, is selling non-core assets including its operations in Indonesia and Thailand to focus on the North Malay basin. On Tuesday, it agreed to sell its Russian unit to Lukoil for $2.05 billion..
Newfield Exploration Co, which is battling a drop in production, is selling its China and Malaysia gas fields, which analysts and bankers estimate could fetch between $1-$1.5 billion. Asia bidders are said to be interested in that asset as well.