Canonsburg — Columbia Gas announced Friday that more than 350,000 customers will receive a one-time credit following an annual review of its gas purchases.

This would include customers in Butler County.

The average residential customer will receive a one-time credit of about $170, which is based on actual usage from Oct. 1, 2008 through Sept. 30, 2009, according to a Columbia Gas news release.

The Pennsylvania Public Utility Commission approved a Columbia Gas request to allocate more than $77 million to customer's accounts, based on the amount of natural gas bought from Columbia Gas between Oct. 1, 2008, and Sept. 30, 2009.

Each year, gas utilities in Pennsylvania must conduct a review of their gas costs. Part of that review involves the determination of whether there is a need to charge customers to recover undercollected gas costs or to provide a credit based on over-collections for the prior year.

By law, gas utilities cannot make a profit on the natural gas they sell to customers, but they are permitted to recoup the actual costs incurred in buying the natural gas, according to the news release.

This year, natural gas prices dropped significantly after the January 2009 quarterly rate adjustment. This credit makes certain that customers receive the benefit of the lower-than-expected gas prices.

Typically, such credits are allocated over a 12-month period on a customer's bill.

However, to ease the impact of winter bills during the current economy, Columbia Gas filed a request with the PUC on Sept. 17, 2009, requesting permission to apply a one-time, lump-sum credit to its customers' bills in November.