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July 20 (Reuters) - Magnolia Oil & Gas MGY.N said on Monday it had agreed to acquire WildFire Energy for about $4.06 billion, including debt, to expand its position in the Giddings field in South Texas.

The deal, includes about 810,000 net acres in Giddings and would lift the company's pro forma position there to more than 1.25 million net acres, spanning the Austin Chalk, Eagle Ford and Woodbine formations.

The acquisition also includes a sand mine that supplies about 80% of Magnolia's annual sand needs, along with more than 500 miles of gas gathering pipelines.