If you're one of Rocky Mountain Power's 144,511 customers in Wyoming, your monthly electricity bill may soon increase   again.

For the second year in a row, the utility   a division of Warren Buffet's PacifiCorp   says it underestimated costs for coal and natural gas to fuel power plants and to buy electricity on the open market, and it wants to tap Wyoming ratepayers to make up the difference.

Rocky Mountain Power on Monday filed for a 12.3% rate increase that   if approved   would tap Wyoming customers for a one-time $86.4 million, mostly due to higher-than-expected fuel costs in 2023. If Wyoming regulators approve the full amount, the company's typical residential customer will experience a 9.3% increase, or about $12 more to their monthly bill, beginning July 1 and lasting for 12 months, according to Rocky Mountain Power.

The utility's large industrial customers in the state   trona mines, oil and natural gas refineries, for example   consume about 70% of the electricity it provides in Wyoming and would pay a higher percentage, according to filings with the state.

In another request filed earlier this month, Rocky Mountain Power is asking permission to cancel a ratepayer credit derived from the President Donald Trump-era Tax Cuts and Jobs Act because it is set to expire, resulting in another 4.2% hike, or about $29.9 million.

That's not all.