Mountain Fuel Supply Co. surpassed its record for firm deliveries of natural gas on three consecutive days in December.

The company delivered 620 million cubic feet on Dec. 22, 665 million cubic feet on Dec. 23 and 650 million cubic feet on Dec.24, equaling or surpassing the record 620 million cubic feet set in February 1988.Firm customers are residential and commercial users who are guaranteed service without interruption during peak-demand periods.

Mountain Fuel, a subsidiary of Questar Corporation, serves about 500,000 customers in Utah, southwestern Wyoming and southeastern Idaho.

Salt Lake City recorded an all-time record low maximum temperature of 2 degrees on Dec. 22. Numerous record low daily maximum and minimum temperatures were set in the Mountain Fuel service area from Dec. 20-31. The record December deliveries partially offset the impact of warmer-than-normal temperatures that occurred through the first 11 months of the year, a company press release said.

Mountain Fuel also reported that its 1990 earnings are expected to meet or surpass financial market expectations.