Questar Corp., parent company of Mountain Fuel Supply Co., reports earnings of $33.05 million or $1.70 per share for the first quarter, up 14 percent over the $28.97 million or $1.45 per share earned in the same period last year.

Average shares of common stock outstanding was 19.27 million for the quarter, down from 19.75 million in the first three months of 1990.Questar credits the earnings jump to increased retail natural gas deliveries, higher oil prices and expanded gas-marketing activities.

Mountain Fuel Supply Co. had net income of $19.08 million during the 1991 quarter compared to $15.32 million a year earlier. Total deliveries increased 14 percent.