Almost 2 million natural gas customers in Washington can expect to see lower heating bills this winter due to a decrease in wholesale natural gas costs.

The Washington Utilities and Transportation Commission on Thursday approved requests by the state’s four investor-owned natural gas companies to reduce rates for customers beginning Nov. 1.

Natural gas companies in Washington are required to adjust rates periodically to reflect changes in wholesale prices. More than half to about two-thirds of a customer’s monthly bill is attributable to the cost of natural gas on which the company is not allowed to earn a profit. The remaining 45 percent covers the cost of delivering the natural gas.

Puget Sound Energy’s average western Washington residential natural gas customer using 68 therms a month will realize a drop of 7.1 percent, or $5.82, to $76.59.

The rates could be subject to further revision. Commission staff will be reviewing the wholesale costs and purchasing and hedging practices of all four natural gas companies in Washington to ensure that they are appropriate in current market conditions.

The commission decision made today on Avista’s natural gas rate request is separate from the general rate case filed by the company in April. The UTC is expected to make a final decision in that proceeding next March.

The utilities distribute natural gas to customers but do not produce their own fuel. About half of Washington’s natural gas supplies come from the Canadian provinces of Alberta and British Columbia and the other half from Rocky Mountain production sites such as Wyoming.

Bellevue-based Puget Sound Energy serves more than 785,000 natural gas customers in parts of Snohomish, King, Pierce, Lewis, Thurston and Kittitas counties.