Private equity firm Quantum Energy Partners will invest up to $1 billion in a new entity for acquisition and development of oil and gas assets that will be managed by Linn Energy LLC. Linn will be able to take a 15-50 percent direct working interest in the acquired assets, the two companies said in a joint statement on Monday. Linn's shares rose 4.5 percent in premarket trading, while its unit LinnCo LLC's shares were up 6.5 percent.