RIL, which bought 45 per cent interest in Pioneer Natural Resources Co's Eagle Ford shale formation of south Texas for USD 1.3 billion, is working with Citigroup Inc and Bank of America Merrill Lynch to find a buyer, industry sources said. Pioneer holds 46 per cent in the Eagle Ford venture while the remaining 9 per cent is with Alpha SAB's Newpeck LLC. Newpek too is exploring opportunities to sell its share and is being advised by Tudor Pickering Holt & Co. RIL is also selling its investment in EFS Midstream LLC, an oil and gas gathering treatment and transportation network, sources said. EFS Midstream operates 11 central gathering plants in south Texas.