(Adds reaction from Reliance and Pioneer) By Angel Gonzalez and Jason Womack Of DOW JONES NEWSWIRES HOUSTON (Dow Jones)--India's Reliance Industries Ltd. (500325.BY) agreed to buy 45% of Pioneer Natural Resources Co.'s (PXD) acreage in the Eagle Ford natural-gas shale for $1.35 billion, a person familiar with the deal said Tuesday. Dallas-based Pioneer has about 310,000 acres in the south Texas gas field, where the company had successfully drilled five wells as of May. The move means that Reliance is doubling down on North America's fast-growing shale-gas business. In April, the conglomerate agreed to buy a stake of Atlas Energy Inc.'s (ATLS) Marcellus Shale acreage for $1.7 billion. The Marcellus Shale is a giant rock formation underlying Pennsylvania, New York and other states. Pioneer spokeswoman Susan Spratlen said that the company has been seeking a joint-venture partner for its Eagle Ford assets, but added that she "cannot comment further on that process at this time. We do not comment on rumors." The company hopes to announce the results of the process by the end of June, she said in an e-mail. A Reliance spokesman declined to comment. In recent years, North American independent gas producers have learned how to crack the tight rock formations known as shale using streams of water and chemicals. The development fueled an unprecedented boom in U.S. gas production, and lured international companies such as Reliance, Total S.A. (TOT) and Statoil ASA (STO). Investment from these companies helps independents like Pioneer keep drilling despite restricted cashflow from low natural-gas prices. The Eagle Ford Shale is an oil- and natural-gas-bearing rock formation that has recently been the site of frenzied development. The area is rich with gas, and has drawn the attention of some profit-seeking producers who aim to expand their output of oil and natural-gas liquids. Earlier this year, BP PLC (BP) said it had acquired a stake in the field from privately-held Lewis Energy. Chesapeake Energy Corp. (CHK) is looking for a partner to jointly develop its 500,000 acres in the Eagle Ford. -By Angel Gonzalez, Dow Jones Newswires; 713-547-9214;angel.gonzalez@dowjones.com (Santanu Choudhury contributed to this story) (END) Dow Jones Newswires June 22, 2010 13:20 ET (17:20 GMT)