Permian Basin heavyweight Concho Resources Inc., now in a quiet period as the mega-merger with ConocoPhillips is readied, said its oil and gas production, along with profits, declined in the third quarter.

Earlier this month, Houston-based ConocoPhillips clinched an all-stock takeover of Concho worth $9.7 billion. The Midland, TX-based independent is the fifth-largest producer in the Permian.

Concho’s third-quarter results issued on Tuesday were abbreviated because of the merger, which is set to be completed by early next year.

Total production fell year/year by around 10,000 boe/d, averaging 320,000 boe/d. Oil output declined to 201,000 b/d from 204,000. Natural gas production fell to 716 MMcf/d from 764.

However, controllable costs, which include production and...