* 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 doublesin 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 NationalPetroleum Corp and Malaysia's Petronas are considering bids forMarathon Oil Corp's stakes in two Angolan offshore oiland gas fields, people familiar with the matter told Reuters.
The sale comes as U.S. oil and gas producers scale backtheir global ambitions to focus on their home market, openingthe field for Asia's state-backed giants. An estimated $6billion worth of oil and gas blocks are being sold by companiesworldwide, according to ThomsonReuters data.
Houston-based Marathon first laid out plans in late 2011 todivest up to $3 billion worth of assets to plough money backinto other operations.
Marathon has put its entire 10 percent stake each in Blocks31 and 32 offshore Angola up for sale, the people said. The twoAsian energy companies are working with advisors to place bids,though no deal was imminent, they added.
BP, Total SA and Angolan state energycompany Sonangol are among Marathon's partners.
Marathon, CNPC and Petronas declined to comment. Sourcesdeclined to be identified as the sale process is confidential.
Africa is emerging as the new frontier for oil and gasexploration, with early investors often cashing out.
With Asian acquirers turning aggressive, their share inglobal oil and gas deals has more than doubled from a decadeback, according to Thomson Reuters data. Asia's share in globaloil and gas M&A climbed to 19.6 percent in 2012, from 7.6percent in 2003, the data shows. This comes as global oil andgas M&A jumped to a record $345.9 billion last year.