Pioneer, which has about 230,000 acres in the Eagle Ford Basin according to its website, sold a 45% interest in the property to Reliance for $1.2 billion in 2010. The Eagle Ford Basin asset is a three-way joint venture between Mumbai, India-based Reliance; Irving, Texas-based Pioneer, and a division of Mexico's Alpha SAB de CV.

Reliance has appointed Citigroup Inc and Bank of America Merrill Lynch to help sell its 45% stake, the sources said, asking not to be named because the matter is not public.

Representatives for Citi and Bank of America declined to comment, while Reliance could not be immediately reached for comment.

The property for sale produces 115,000 barrels of oil equivalent per day, with 60% of the production in liquid form rather than gas, one of the people said.

There are 472 wells on the Eagle Ford property, according to a Reliance presentation from July. Pioneer owns 46% of the joint venture, with Alpha SAB's Newpeck LLC owning 9%.

As part of its planned exit from the Eagle Ford joint venture, Reliance is also selling its investment in EFS Midstream LLC, an oil and gas gathering treatment and transportation network, the people said. The mid-stream joint venture was initially funded by Pioneer and Reliance in June 2010.

EFS Midstream operates 11 central gathering plants in south Texas, according to the company's website.

The sale process for the oil production assets and the oil and gas gathering assets is at an early stage, the people said.

Pioneer is the operator of the wells in the joint venture, which could complicate the sale process, one of the people said. The company is an independent oil and natural gas exploration and production company with operations in several US regions.