O'ahu residential electricity rates will increase for the first time since September as per-kilowatt-hour prices creep up slightly from May's rate.

Hawaiian Electric Co. said the typical 600-kilowatt-hour residential bill on O'ahu will rise to $120.36 from $117.45 in May.

The effective rate for electricity in Honolulu will rise to 18.63 cents per kilowatt hour from the 18.15 cents charged last month.

The O'ahu rate hit a high of 32.5 cents per kilowatt hour in September.

Elsewhere in the state:

• Maui customers will see their rates rise to 23.14 cents from 21.88 cents in April.

• Big Island residential rates will rise to 29.21 cents per kilowatt hour from 29.07 cents.

• Kaua'i Island Utility Cooperative's May rate is 25.33 cents, up from 25.43 cents last month.

Rates spiked in Hawai'i last year because most of the electricity is produced using petroleum products such as fuel oil or diesel oil, which rose in cost.

On O'ahu, rates peaked in September, when residential customers' monthly bill averaged $202.13.