Breitburn Energy is buying QR Energy LP in a deal worth about $1.46 billion.
QR unitholders will receive approximately 72 million common units of Breitburn Energy Partners LP, or 0.9856 of a Breitburn unit, for each unit of QR Energy that they own. The consideration to be received by QR unitholders is valued at $22.48 per unit, a 19 percent premium to Wednesday's closing price of $18.87.
Shares of Houston's QR Energy are up more than 8 percent Thursday in premarket trading.
The companies put the transaction's value at approximately $3 billion, which includes QR's existing debt and outstanding convertible preferred units.
The boards of both companies have unanimously approved the deal, which is targeted to close later this year or in early 2015.
Breitburn is based in Los Angeles.