Oxygen scored hefty ratings with the premiere of “Mo’Nique’s FAT Chance,” its full-figured beauty competition, the network said Tuesday. The debut Aug. 6 was Oxygen’s highest-rated original telecast ever with a 1.1 household rating, up 176 percent from the Aug. 2004 time period average. A repeat of the program on Aug. 7 drew a 1.0 rating, making it Oxygen’s second-highest-rated original in the network’s history.