Questar Corp.'s non-utility natural gas reserves increased 17 percent in 1990 while the cost of finding new gas reserves fell significantly.

The Salt Lake City-based company's reserves on Dec. 31 totaled 140 billion cubic feet compared with 119 bcf one year earlier. About half the increase resulted from new discoveries while the other half came from an expanded reserve acquisition program. Actual gas production rose from 10.9 bcf in 1989 to 13.5 bcf last year, contributing to a 58 percent improvement in net income for Questar's exploration and production efforts. The company sold about 1.5 bcf to improve operating efficiencies.Questar's oil reserves dropped 8 percent in 1990 to 11.7 million barrels. Celsius Energy Co. and Universal Resources Corp., Questar subsidiaries, increased reserves by 500,000 barrels to 5.6 million barrels. Reserves owned by Wexpro Co., another subsidiary, were reduced 1.5 million barrels to 6.1 mill due to the normal decline and production performance of older fields.

Gas supplies owned by Questar's retail gas distribution utility, Mountain Fuel Supply Co., increased 3 percent to 375 bcf at the end of 1990. Development drilling and other efforts added 36 bcf at an average cost of 49 cents per thousand cubic feet.

Questar's five year average finding cost, including utility reserve additions, was $6.04 per barrel compared with $6.47 in 1989. The 1990 finding cost was $3.65 per barrel. The company achieved a 40 percent success ratio in its exploratory drilling efforts, substantially above the national average. And 94 percent of the development drilling operations succeeded.

Questar, through its subsidiaries, engages in oil and gas exploration and production, interstate natural gas transmission, retail natural gas distribution and telecommunications.