Questar purchases about half the gas it supplies customers on the open market. The other half comes from company-owned wells. And although natural gas from Questar's company-owned supplies has been consistently affordable, market-gas prices skyrocketed earlier this year, forcing the company to increase rates.

Over the past several months, however, market-gas costs have gone down based on increased supplies, lower demand for gas and other economic factors. This change allows Questar Gas to pass the savings on to customers.

This decrease request was made in a special-out-of-period gas-cost-adjustment or "pass-through" filing. Such filings enable the company to reduce rates immediately to reflect changes in gas-supply costs.

With the PSC's approval of the decrease, the annual bill for the typical residential customer using 115 decatherms per year changes from $905.02 to $767.02. This is a decrease of $138 per year or about 15 percent.