Retail natural gas utility bills will be up 2-4% this summer in Colorado, according to a filing on Wednesday to state regulators by Xcel Energy Inc.'s Denver-based combination utility, Public Service Company of Colorado. The rise comes despite the fact that gas commodity prices decreased for 3Q2016 compared to the same period last year. The higher monthly bills are caused by increases in other costs that were captured in a general rate case that went into effect early this year. Gas commodity costs for the third quarter are 33 cents/therm for residential customers, compared to 34.2 cents/therm for the same period last year; for small businesses the rate is 32.7 cents/therm in 3Q2016, compared to 33.89 cents/therm for with 3Q2015. Average bills are estimated to be $22.02/month for residential customers and $82.25 monthly for small businesses, compared to $21.18 and $80.60 for residential and small business customers, respectively, last year in the same quarter.