QR Energy LP  agreed to pay $557 million in a cash-and-unit transaction to acquire oil and natural- gas properties from Quantum Resources Funds, a deal that more than doubles the company's production capacity and reserves.

The company, a limited partnership formed to own and acquire oil and natural-gas properties, agreed to pay Quantum Resources Funds $227 million in cash from borrowings under an existing bank credit facility and the issuance of $350 million of convertible preferred units at a par value of $21 a unit. The deal is expected to close on or about Oct. 1.

The properties are located in existing core areas including Permian Basin, Ark-La-Tex and Mid-Continent. The assets have more than 1,500 producing oil and natural-gas wells, and net production in the fourth quarter is expected to total 8,000 barrels of oil equivalent a day.

"The properties are located in our existing core areas and offer an inventory of low risk development projects that will supplement our production in the years to come," said Chief Executive Alan L. Smith.

QR Energy owns properties consisting of mature, legacy onshore oil and natural-gas reservoirs with predictable production profiles. The company, which was formed by affiliates of Quantum Resource Funds, went public late last year.

The company's units were inactive in premarket trading after closing Friday at $17.13.