Oahu residents will see their electrical bills rise marginally this month while customers in Maui County and on Hawaii island will see some financial relief.

Hawaiian Electric Co. said Thursday that the typical HECO bill in December for an Oahu household using 500 kilowatt-hours of electricity is $141.82, or 26.3 cents a kilowatt-hour, up $2.30 from $139.52, or 25.9 cents a kilowatt-hour, in November.

Barring a big drop in fuel costs, those rates likely will be higher next year once HECO implements the base-rate increase that was approved Dec. 15 by the state Public Utilities Commission. HECO said this week it is unhappy with the small interim 2.5 percent increase that was approved and intends to file a motion for reconsideration.

HECO initially had sought a 6.9 percent increase and then lowered that amount to 3.5 percent after reaching a settlement with the state consumer advocate.

Maui Electric Co. residential customers on Maui island using 500 kilowatt-hours will see their bills drop $12.67 to $145.51, or 27.2 cents a kilowatt-hour, compared with $158.18, or 29.7 cents a kilowatt-hour. The drop will be welcome news after MECO customers saw their bills jump $19.94, or 14 percent, the previous two months.

MECO customers on Molokai using 400 kilowatt-­hours will pay an average $150.36, or 35.2 cents a kilowatt-hour. That is down $2.71 from $153.07, or 35.8 cents a kilowatt-hour, in November.

Lanai residents using 400 kilowatt-hours will pay an average of $149.55, or 35 cents a kilowatt-hour. That is lower by $4.35 from $153.90, or 36.1 cents a kilowatt-hour, last month.

Bills on Lanai and Molokai are calculated based on a typical household using 400 kilowatt-hours of electricity in a month. This is due to lower energy use compared with Maui, Hawaii island and Oahu, HECO said.

The average cost in December for Hawaii Electric Light Co. residential customers using 500 kilowatt-hours is $175.02, or 32.7 cents a kilowatt-hour. That is down $2.58 from $177.60, or 33.2 cents a kilowatt-hour, in November. Over the previous two months, HELCO customers had seen their bills rise $6.08, or 3.5 percent.

HECO, MECO and HELCO monthly bills include the cost for kilowatt-­hours used in addition to other charges.

“On Oahu, typical residential bills increased slightly due to higher fuel and purchased power energy costs,” HECO spokeswoman Shannon Tangonan said. “On Maui, lower fuel costs and lower purchased power energy costs contributed to the decrease in typical residential bills. Lower fuel costs caused typical residential bills to dip on Hawaii island, Lanai and Molokai.”

Fuel prices dictate electrical bills, as HECO’s energy mix is primarily made up of oil. In 2016, HECO’s energy mix was roughly 67.9 percent oil on Oahu. HECO imports oil primarily from Southeast Asia and the Middle East. The remainder of the energy comes from coal, 21.4 percent; solid waste, 6 percent; wind, 3.4 percent; solar, 0.8 percent; and biofuel, 0.5 percent.

The Kauai Island Utility Cooperative’s effective rate decreased to 32.98 cents a kilowatt-hour in December from 33.36 cents a kilowatt-­hour in November. The typical bill for a household using 500 kilowatt-­hours in December is $175.48, including a $10.58 customer base charge. In November, the bill was $1.91 higher at $177.39.

The cost of electricity in the state is more than double the national average, as Hawaii residents paid an average of 29.03 cents a kilowatt-hour for electricity in September. The national average was 13.3 cents in the same month, according to the U.S. Energy Information Administration.