<Page> Exhibit 12 Questar Gas Company Ratio of Earnings to Fixed Charges (Unaudited) <Table> <Caption> 12 Months Ended March 31, 2002 2001 ------- ------- (Dollars in Thousands) Earnings Income before income taxes $40,538 $41,903 Plus debt expense 23,623 21,747 Plus allowance for borrowed funds used during construction 302 969 Plus interest portion of rental expense 743 737 ------- ------- $65,206 $65,356 ======= ======= Fixed Charges Debt expense $23,623 $21,747 Plus allowance for borrowed funds used during construction 302 969 Plus interest portion of rental expense 743 737 ------- ------- $24,668 $23,453 ======= ======= Ratio of Earnings to Fixed Charges (1) 2.64 2.79 </Table> (1) For the purposes of this presentation, earnings represent income before income taxes and fixed charges. Fixed charges consist of total interest charges, amortization of debt issuance costs and losses from reacquiring debt, and the interest portion of rental costs, estimated at 50% for the purpose of this calculation.