Electric customers in southern Maine will learn Monday how much, or if, rates will rise in 2019.

Earlier this week, a nearly 16 percent increase in the supply cost of electricity was approved for consumers in northern and eastern Maine who choose a default electric rate, called the standard offer. Those customers are serviced by Emera Maine, which delivers electricity in the region. The standard offer for customers who live in Central Maine Power’s delivery area will be announced Monday.

The new rates are only for the energy-supply portion of electricity bills, not the distribution services provided by Emera and CMP. Under Maine’s 19-year-old electric restructuring law, utilities only distribute power, they don’t generate and sell it. Total electric bills in southern Maine currently average about $88 per month, a combination of the supply and distribution charges.

It’s difficult to predict if rates for customers of Emera Maine and CMP will move in the same direction. Earlier this year, for instance, the standard offer for customers of Emera Maine increased 14 percent, while the rate for CMP-area customers rose 18 percent. Last year, southern Maine standard offer rates rose 3.5 percent, while the standard offer price for customers served by Emera Maine dropped 4.6 percent. The year before that, standard rates dropped less than 1 percent in the northern part of the state while southern customers saw the standard offer tumble by 13.4 percent.

For the typical northern Maine customer who lives in the Emera Maine service area, bills will jump nearly $6 a month because of the increase in the cost of electricity supplied under the standard offer. Delivery costs remain the same.

The PUC announced Tuesday that the standard offer for residential and small-business customers within Emera Maine‘s delivery area will rise by 15.8 percent on Jan. 1, 2019. Rates for midsize businesses differ by month but are expected to rise by about 11.4 percent overall in the next year. Rates for large businesses are set monthly based on market prices.

The overall bills for residential and small-business customers in northern Maine will go up by about 6.5 percent. The average Emera Maine customer pays $90.48 a month for electricity and delivery charges, the company said, so the increase caused by the higher electricity supply charges will be about $5.88 a month.

Rates are expected to rise because of price increases in the wholesale electric supply market in New England, but the PUC won’t get the bids for CMP-area standard offer electricity rates until Monday.

Mitchell Tannenbaum, a PUC staff member, said delivery costs in northern Maine are slightly higher than those in southern Maine and make up a larger portion of a customer’s overall bill. Because delivery rates won’t change until next summer, that portion of the bill stays flat for now and will offset some of the percentage increase in the supply rates.

The vast majority of CMP customers choose the standard offer for the supplier of their electricity. As recently as 2012, 40 percent of customers chose a supplier other than the standard offer, but that percentage has dropped in recent years.