<Page> Exhibit 12 Questar Gas Company Ratio of Earnings to Fixed Charges (Unaudited) <Table> <Caption> 12 Months Ended September 30, 2001 2000 ------- ------- (Dollars in Thousands) Earnings Income before income taxes $43,077 $25,656 Plus debt expense 23,341 21,106 Plus allowance for borrowed funds used during construction 807 221 Plus interest portion of rental expense 772 666 ------- ------- $67,997 $47,649 ======= ======= Fixed Charges Debt expense $23,341 $21,106 Plus allowance for borrowed funds used during construction 807 221 Plus interest portion of rental expense 772 666 ------- ------- $24,920 $21,993 ======= ======= Ratio of Earnings to Fixed Charges (1) 2.73 2.17 </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.