The typical household bill for Oahu residents in August declined $1.65 from what they paid the previous month.

Hawaiian Electric Co.’s bill for an Oahu household using 500 kilowatt-hours was $140.14, or 26.0 cents a kilowatt-hour, down from $141.79, or 26.3 cents a kilowatt-hour, in July. HECO spokeswoman Shannon Tangonan said the lower bills on Oahu were due to reduced fuel prices.

Fuel prices dictate the utility bills, as HECO’s energy mix is primarily made up of oil. In 2015 HECO’s energy mix was roughly 71.1 percent oil on Oahu. HECO imports oil primarily from Southeast Asia and the Middle East.

The owner of HECO and its sister utilities in Hawaii and Maui counties spent $141.2 million on fuel in April through June. This is up from the $91.9 million it spent during the same period in 2016. This month, customers were affected by fuel purchases made in June and July, as it takes about one to two months for the cost of the fuel that HECO buys to show up on customers’ bills, according to Tangonan.

While the utility said fuel prices helped cut costs for residents during August, the price of oil has been pointed to by Hawaii’s energy community as the main reason the cost of electricity is so high on the islands compared with the rest of the nation. The cost of electricity in the state is more than double the national average, as Hawaii residents paid an average of 29.07 cents a kilowatt-hour for electricity in May. The national average was 13.02 cents in the same month, according to the latest figures from the U.S. Energy Information Administration.

Electrical utility customers on Maui saw a larger decrease in bills in August.

Maui Electric Co. customers saw bills drop about $11. The average bill for a Maui household using 500 kilowatt-hours was $145.30, or 27.1 cents a kilowatt-hour, down from $156.51, or 29.4 cents a kilowatt-hour, in July.

“Maui customer bills were affected by less purchased power (wind) in the production mix, as well as lower fuel costs,” Tangonan said.

Customers on Molokai and Lanai also saw lower bills in August compared with July. MECO customers on Molokai using 400 kilowatt-hours of electricity are paying an average of $134.08, or 31.1 cents a kilowatt-­ hour, down from $138.83, or 32.3 cents a kilowatt-­hour in July. Lanai residents using 400 kilowatt-hours of electricity are paying $140.36, or 32.7 cents a kilowatt-hour, down from $142.28, or 33.2 cents a kilowatt-hour. 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.

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

The residential cost for Hawaii Electric Light Co. customers’ August electrical bill was $160.39, or 29.7 cents a kilowatt-hour, up from $158.79, or 29.4 cents a kilowatt-hour, in July.

The Kauai Island Utility Cooperative’s rate fell to 31.04 cents a kilowatt-hour in August. In July the rate was 31.20 cents a kilowatt-hour. The typical bill for a household using 500 kilowatt-­hours in August is $165.77, including a $10.58 customer base charge. In July the bill was $166.61.