Ameren rates will be going up. The question is: Who will pay, and how much?

The state authorized Ameren last month to raise rates enough to boost revenue by nearly 9% or about $220 million a year. The parties discussed at a hearing on Thursday how to divide the costs between residential and industrial customers.

“It’s just a matter of how do you split the pie,” said John Coffman, a lawyer who advocates on utility issues for the Consumers Council of Missouri, describing the case ahead of the hearing. “That’s the one main issue that has not been resolved.”