Hawaiian Electric Co. customers on Oahu saw an uptick of more than a dollar in their electrical bills in May, following a smaller increase in April.

The bill for a typical household using 500 kilowatt-hours on Oahu will be $124.85 this month, $1.51 higher than what customers paid in April. The price per kilowatt-hour on Oahu was 22.9 cents, which was flat with April rates.

Darren Pai, HECO spokesman, said the utility had to pay more for energy from third-party generators, and that caused customer electric bills to rise.

Maui and Big Island ratepayers will see a drop in their May bills.

“On Oahu, bills are slightly higher due to higher costs for power purchased from independent power producers,” Pai said.

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 26.77 cents a kilowatt-hour in February, while the national average was 12.15 cents in the same month.

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

“Overall, typical residential bills remain lower than in past years, primarily due to lower fuel costs,” Pai said. “However, each island has a slightly different situation this month. We are working to provide our customers with lower and more stable bills through many steps, including transitioning to 100 percent renewable energy.”

The residential rate for Hawaii Electric Light Co. customers on the Big Island was 27 cents a kilowatt-hour, down from the 27.8 cents a kilowatt-hour residents paid in April. The average bill this month for a household using 500 kWh is $146.66, down from $150.76.

Bills are lower on the Big Island because of a credit received from an independent power producer, Pai said.

Maui customers paid 24.6 cents per kilowatt-hour, down from 26.1 cents in April. A household using 500 kWh will pay $132.89, down from $140.37 last month.

“Bills are lower on Maui due to lower fuel costs and less expected wind generation (currently, oil prices are lower than wind energy prices),” Pai said. “However, bills are higher on Lanai and Molokai due to higher costs for diesel fuel, which is used on those islands.”

The Kauai Island Utility Cooperative increased its rate to 30.9 cents a kilowatt-hour in April from 29.8 cents a kilowatt-hour in March. The bill for a household using 500 kWh of electricity, including a $10.58 customer base charge, is $165.08, up from $159.58.

Maui Electric Co. customers on Molokai using 400 kWh of electricity will pay an average of $120.31 with effective rates of 27.6 cents a kilowatt-hour, up from 27.3 cents a kilowatt-hour in April, when the typical bill was $118.92. Customers on Lanai using 400 kWh of electricity will pay 30.6 cents a kilowatt-hour, up from 29 cents a kilowatt-hour in March. Lanai residents will pay $132.03 in May compared with $125.90 in April.

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

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