Oahu residents’ electrical bills ticked up slightly in June after dipping $3 in May.

Hawaiian Electric Co.’s bill for an Oahu household using 500 kilowatt-hours rose $1.47 from May to $141.89, or 26.3 cents a kilowatt-hour. Last month’s bill of $140.42 was lower than April’s $143.45 average.

HECO spokeswoman Shannon Tangonan said the increase on Oahu was primarily due to higher costs for power purchased from outside sources.

On Oahu half of the energy HECO uses is bought from eight independent power producers. The independent power producers include AES Hawaii, a coal-fired facility in Kapolei, and the Kahuku Wind facility on the North Shore.

The cost of electricity in the state is more than double the national average, as Hawaii residents paid an average of 29.04 cents a kilowatt-hour for electricity in March. The national average was 12.90 cents in the same month, according to the latest figures from the U.S. Energy Information Administration.

The higher cost of electricity in Hawaii is widely attributed to the state’s use of fossil fuels. 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.

Neighbor island residents also saw bills jump in June. Wind power costs pushed up bills nearly $15 on Maui, while fuel costs caused Big Island residents’ bills to rise $8.

The residential cost for Hawaii Electric Light Co. customers on Hawaii island is $168.82, or 31.4 cents a kilowatt-hour, in June, up from $160.30, or 29.7 cents a kilowatt-hour in May.

Tangonan said the jump for Big Island bills is tied to the higher price of fuel, which causes the costs of all power producers on the island to increase.

“Prices paid to independent power producers that sell wind, geothermal and hydroelectric power are also tied to the price of oil,” she said.

Rising fossil fuel costs and strong wind caused Maui Electric Co. customers to see bills increase $14.82. Because of the contract with wind producers on the island, MECO has to buy wind energy that is available. In June the wind power cost about 19 cents a kilowatt-hour, versus 13 cents a kilowatt-hour for power from oil-fired plants.

If the price of oil goes up, wind could become relatively cheaper, but for now, oil-fired plants are cheaper.

The average bill for a Maui household using 500 kilowatt-hours was $159.61, or 30 cents a kilowatt-hour, in June. In May the bill was $144.79, or 27.0 cents a kilowatt-hour.

Customers on Molokai and Lanai also paid higher bills in June compared with May.

MECO customers on Molokai using 400 kilowatt-hours of electricity are paying an average of $139.44, or 32.4 cents a kilowatt-­hour. In May the bill was $137.47, or 31.9 cents a kilowatt-hour.

Lanai residents using 400 kilowatt-hours of electricity are paying $143.14, or 33.3 cents a kilowatt-hour. In May, residents paid $139.14, or 32.3 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, plus other charges.

The Kauai Island Utility Cooperative’s rate fell to 31.42 cents a kilowatt-hour in June. In May the rate was 32.11 cents a kilowatt-hour. The typical bill for a household using 500 kilowatt-­hours in June, including a $10.58 customer base charge, is $167.70.