Hawaiian Electric Co. customers on Oahu saw April’s electrical bills slightly increase following a six-year low in March.

The bill for a typical household using 500 kilowatt-hours on Oahu will be $123.34 this month, 28 cents higher than what customers paid in March. The price per kilowatt-hour on Oahu was 22.6 cents a kilowatt-hour, which was flat with March rates.

Despite the higher monthly cost, the bill for an Oahu household is down 12.5 percent from April of last year.

“Bills were up slightly on Oahu due to a slight increase in the cost of purchasing energy from independent power producers,” HECO spokesman Darren Pai said Monday. “Overall, customers are benefiting from low oil prices as bills remain low compared to recent years. To ensure long-term savings for our customers, it’s critical that we keep focused on achieving 100 percent renewable energy.”

Hawaii has the highest electrical rates in the nation, due in part to the state’s use of imported oil for most of its power. Hawaii’s price of electricity is more than double the national average, according to the latest figures from the U.S. Energy Information Administration. Hawaii’s residents paid an average of 26.92 cents a kilowatt-hour in January, while the national average was 12.01 cents in the same month.

In 2014 oil made up roughly 71.3 percent of the energy mix of HECO and its subsidiaries on Maui and Hawaii island. HECO imports oil mainly from Southeast Asia and the Middle East. Other states use natural gas, hydro­electric power, coal or nuclear power, which keeps costs low.

Maui Electric Co. customers saw an increase in rates for the second month in a row because the contracted price for wind energy is higher than the cost of using oil to generate electricity.

“As we saw last month, bills on Maui were up slightly due to higher amounts of wind power, which has a higher contracted cost than the current cost of oil-based generation,” Pai said.

Maui customers paid 26.1 cents per kilowatt-hour, up from 25.9 cents in March. A household using 500 kilowatt-hours will pay $140.37, up from $139.17 last month.

The residential rate for Hawaii Electric Light Co. customers on the Big Island was 27.8 cents a kilowatt-hour, down from the 28.5 cents a kilowatt-hour residents paid in March. The average bill this month for a household using 500 kilowatt-hours is $150.76, down from $154.26.

The Kauai Island Utility Cooperative increased its rate to 29.8 cents a kilowatt-hour in April from 28.7 cents a kilowatt-hour in March. The bill for a household using 500 kilowatt-hours of electricity, including a $10.58 customer base charge, is $159.58, up from $154.08.

Maui Electric Co. customers on Molokai using 400 kilowatt-hours of electricity will pay an average of $118.92 with effective rates of 27.3 cents a kilowatt-hour, down from 28.2 cents a kilowatt-hour in March, when the typical bill was $122.61. Customers on Lanai using 400 kilowatt-hours of electricity will pay 29 cents a kilowatt-hour, up from 28.6 cents a kilowatt-hour in March.

Lanai residents will pay $125.90 in April compared with $124.12 in March.

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

Monthly bills include the cost for kilowatt-hours used plus other charges.