Oahu’s roller coaster of electricity bill prices has continued into August with the typical residential customer seeing a decline after two months of increases.

Customers’ bills fell $3.70, or 2.5 percent, this month, after climbing in June and July.

The typical residential bill decreased slightly due to lower oil prices, according to Hawaiian Electric Co., the state’s largest utility provider with service to Oahu, Maui and Hawaii island.

The bill for a typical household using 500 kilowatt-hours on Oahu is $142.51 this month, HECO said. The price per kilowatt-hour decreased to 26.4 cents this month from 27.2 cents in July, when the average bill was $146.21.

Hawaii has the highest electrical rates in the nation due in part to the state’s dependence on imported oil for most of its power.

In 2013 oil made up roughly 72 percent of the HECO companies’ energy mix. Other states use natural gas, hydro­electric power or nuclear power to keep costs low.

The latest figures provided by the U.S. Energy Information Administration show that Hawaii’s price of electricity is more than double the national average. Hawaii residents paid an average of 30.21 cents a kilowatt-hour in May, down from 30.54 cents in April. The national average was 12.95 cents in May compared with 12.64 cents in April.

Despite having the highest electrical rates in the nation, the islands have seen a dramatic decrease from rates in 2014, according to data from the Department of Business, Economic Development and Tourism’s State of Hawaii Data Book released Thursday.

August rates for Oahu residents were 9 cents lower than the 2014 average of 35.5 cents a kilowatt-hour.

Most HECO customers on the neighbor islands also are seeing a decrease from their July bills.

The residential rate for Hawaii Electric Light Co. customers on Hawaii island decreased to 32.4 cents a kilowatt-hour from 33.2 cents in July, when the average bill was $178.14. The August bill for a household using 500 kilowatt-hours of electricity is $174.16. August rates for Hawaii island residents were nearly 10 cents lower than the 2014 average of 41.9 cents a kilowatt-hour.

Maui Electric Co. customers using 500 kilowatt-hours of electricity will see a decrease in rates to 30.8 cents per kilowatt-hour from 30.9 cents in July, when the average bill was $164.44. Maui customers will pay an average of $164.11 this month. August rates for Maui residents were 7 cents lower than the 2014 average of 37.8 cents a kilowatt-hour.

The Kauai Island Utility Cooperative lowered its rate to 32.2 cents a kilowatt-hour in August, from 32.7 cents a kilowatt-hour in July. The bill for a household using 500 kilowatt-hours of electricity, including a $10.58 customer base charge, is $171.58, down from $174.08. August rates for Kauai residents were nearly 11 cents lower than the 2014 average of 43.01 cents a kilowatt-hour.

Average monthly usage varies by island, but the 500-kilowatt-hour number is used to make comparisons. Monthly bills include the cost for kilowatt-hours used plus various other charges.

The typical customer bill on Lanai and Molokai is measured with electrical use at 400 kilowatt-hours due to lower energy use, HECO said.

Maui Electric Co. customers on Molokai using 400 kilowatt-hours of electricity will pay an average of $149.83 with effective rates of 35 cents per kilowatt-hour, up from 34.7 cents per kilowatt-hour in July, when the typical bill was $148.55. August rates for Molokai residents were 12 cents lower than the 2014 average of 47.1 cents a kilowatt-hour.

Customers on Lanai using 400 kilowatt-hours of electricity will pay the highest rates in the state at 35.9 cents per kilowatt-hour, a decrease from the 37.1 cents per kilowatt-hour in July. August rates for Lanai residents were nearly 10 cents lower than the 2014 average of 45.80 cents a kilowatt-hour.

Lanai residents will pay $153.70 in August compared with $158.27 in July.

Lower energy prices

Electrical bills by island based on a typical household using 500 kilowatt-hours:

* Customer bills on Lanai and Molokai are measured with usage at 400 kilowatt-hours.