Customers of Columbia Gas of Kentucky will pay 3 percent less for natural gas for the next three months because the state Public Service Commission has approved the utility’s quarterly gas cost-adjustment proposal, which took effect Thursday.

Customers who are supplied by Columbia Gas and have been for the past year will pay $4.1237 per thousand cubic feet, down from $4.2366. People who are now Columbia Gas customers but in the past year were in the Customer Choice program, which uses other suppliers, will pay $5.8574, up from $5.6583.

Columbia Gas adjusts its prices quarterly to reflect market ­conditions. Utilities are not permitted to make a profit on the cost of ­natural gas, which accounts for about half of bills. Gas costs are ­estimated, and actual costs from the same quarter a year ago are reflected in those estimates. The company overestimated its costs and charged more last year, leading to lower prices this quarter for people who were customers a year ago.