Retail natural gas utility bills for residential and small business customers in Colorado are expected to increase 8% in the fourth quarter, compared with the same quarter last year, Xcel Energy’s Denver-based combination utility told Colorado state regulators Monday.

What Xcel officials called “slightly higher prices” are often seen in the last quarter of the year, heading into the winter heating season. The utility asked the Colorado Public Utilities Commission (PUC) to increase both gas and electric utility charges beginning Oct. 1.

By the utility’s estimates, average residential and small business monthly gas bills will be about $65 and $268, respectively, representing about a $5/month hike for residential customers and $20 more each month for small businesses. Upward pressure on wholesale natural gas prices is expected to increase retail charges for the last three months of the year, Xcel told the PUC.

Electric utility rates are expected to see a smaller increase of a little more than 2% for both residential small businesses.

“With minor exceptions, costs associated with increases or decreases through both the electric commodity adjustment [ECA] and gas cost adjustment [GCA] are passed along to customers on a dollar-per-dollar basis,” an Xcel spokesperson said.

Gas rates are going up nearly three cents/therm for both residential and small businesses, hitting 47 cents/therm and 46.75 cents/therm, respectively, Xcel told the PUC. Average residential use is projected to be 89 therms monthly, while small businesses will use an average of 372 therms each.