Natural gas customers of Ameren Missouri will see natural gas rates change under a filing that takes effect tomorrow. This is to reflect estimated changes in the wholesale cost of natural gas as well as a change in the company’s Actual Cost Adjustment (ACA) factor. The ACA factor is a mechanism which tracks any over-collection or under-collection of actual natural gas costs over a 12 month period. The net over- or under-collected balances are subsequently either refunded or collected the next year. Residential customers currently pay approximately $0.47 per Ccf (per hundred cubic feet) of natural gas. Under this filing, the rate will decrease to approximately $0.40 per Ccf. This change will affect Ameren Missouri natural gas customers in areas such as Columbia, Rolla, Salem, Owensville, Jefferson City, Mexico, Wentzville, Cape Girardeau and Marble Hill.