Oahu residents’ electric bills increased in March for the fifth straight month.

Hawaiian Electric Co.’s bill for an Oahu household using 500 kilowatt-hours rose 45 cents from February to $143.26, or 26.6 cents a kilowatt-hour. Last month’s bill of $142.81 was $7.42 higher than January, when the bill was $135.39.

HECO spokeswoman Shannon Tangonan said in an email that Oahu bills ticked up in March because of “higher fuel and purchased power costs.”

The cost of electricity in the state is double the national average, as Hawaii residents paid an average of 27.68 cents a kilowatt-hour for electricity in December. The national average was 12.21 cents in the same month, according to the latest figures from the U.S. Energy Information Administration.

Hawaii’s high rates are largely due to the state’s dependence on imported oil for most of its power — the state spent $5.4 billion on petroleum in 2014, according to the EIA.

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. Other states use a combination of energy resources such as natural gas, hydroelectric power, coal and nuclear power.

Oahu’s neighbor island bills saw higher increases in March.

The residential cost for Hawaii Electric Light Co. customers on Hawaii island is $166.31, or 30.9 cents a kilowatt-hour. March’s bill saw an increase of nearly $4 from $162.87, or 30.2 cents a kilowatt-hour, in February.

Maui Electric Co. customers saw nearly a $5 increase in March due to extra costs at the island’s wind facilities.

“On Maui, the main reason was more purchased power (wind) in the production mix,” Tangonan said.

The average bill for a Maui household using 500 kilowatt-hours is $148.32, or 27.7 cents a kilowatt-hour. In February, the bill was $143.65, or 26.8 cents a kilowatt-hour.

Customers on Molokai and Lanai also paid higher bills in March compared with February.

MECO customers on Molokai using 400 kilowatt-hours of electricity are paying an average of $140.61, or 32.7 cents a kilowatt-­hour. In February, the bill was $137.70, or 32 cents a kilowatt-hour.

Lanai residents using 400 kilowatt-hours of electricity are paying $143.21, or 33.4 cents a kilowatt-hour. In February, residents paid $142.24, or 33.1 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 increased to 33.07 cents a kilowatt-hour in March. In February, the rate was 32.8 cents a kilowatt-hour. The typical bill for a household using 500 kilowatt-hours in March, including a $10.58 customer base charge, is $175.93.