A consortium including South Korea's National Pension Service (NPS) and gas seller E1 Corp has been chosen as preferred bidder to buy a $540 million stake in U.S.-based shale gas transport firm Cardinal Gas Services, NPS and E1 officials said on Monday.

NPS, the world's fourth-largest pension fund, is expected to invest around $250 million, or the biggest portion of the funds needed for the 34 percent stake in Cardinal Gas Services, an NPS spokeswoman said.

An E1 official said although the consortium with NPS had been chosen as preferred bidder, some consortium members as well as the division of stakes within the consortium had yet to be finalised.

The official declined to be identified as they were not authorized to speak to media. A E1 spokesman declined comment.

Cardinal Gas Services, a joint venture between Access Midstream Partners, a U.S.-based Total unit and EnerVest Energy Partners, manages gathering, compression and dehydration for oil and wet gas in the Utica Shale region in Ohio.

Shares in E1 gained 2.9 percent on Monday, beating a 0.5 percent rise in the wider market.