Western Refining Inc. (NYSE: WNR) has acquired a stake in Northern Tier Energy LP (NYSE: NTI) for $775 million.

Ridgefield, Conn.-based Northern Tier Energy is a downstream energy company that focuses on refining, retail and pipeline operations.

The stake is being sold by private equity firms Acon Investments LLC and TPG Capital, which invested about three years ago.

Western Refining now owns 38.7 percent of Northern Tier. The investment allows the company to expand its refining presence.

El Paso, Texas-based Western Refining is a refining and marketing company.

Barclays and J.P. Morgan Securities LLC served as co-financial advisers to Acon and TPG, while Vinson & Elkins provided legal advice.  

The deal follows oil and gas deals by Crestwood Midstream Partners LP (NYSE: CMLP), which closed a deal for Arrow Midstream Holdings LLC in November, and NGL Energy Partners LP (NYSE: NGL), which bought Gavilon LLC.