With winter approaching, customers of Alabama Gas Corp. are going to pay lower rates for heating their homes, the fourth cutback in the past 12 months.

The Birmingham-based utility has notified the Alabama Public Service Commission that it is dropping rates because its supply costs have gone down. Company spokeswoman Susan Delenne said Wednesday the average residential customer's annual bill should go down by $60.22, which is 5.9 percent.

Delenne said the savings come as many customers are starting to use their heaters regularly for the first time this fall. The winter months traditionally produce the largest bills for customers of Alabama Gas.

The PSC allows Alabama Gas to raise and lower its rates automatically when the cost of obtaining natural gas goes up or down. The reduction took effect Sunday. Delenne said it's impossible to say whether rates will remain stable through the winter.

For the average home that uses 51,700 cubic feet of natural gas annually, the cost will drop from $1,020.10 to $959.88, Delenne said.

This is the fourth time since November 2008 that Alabama Gas has lowered rates. David Rountree, spokesman for PSC member Susan Parker, said the typical home has saved $181, or 17 percent, because of those reductions.

The reduction in gas prices also affects businesses, Delenne said.

Alabama Gas, a unit of Energen Corp., serves large portions of central and north Alabama, including Montgomery, Birmingham and Tuscaloosa.