Oahu residential customers will need to dig a little deeper to pay their electricity bills this month.

The bill in August for a typical household using 600 kilowatt-hours went up from July by 94 cents to $218.18, according to data released this week by Hawaiian Electric Cos., the state’s largest utility provider with service to Oahu, Maui and Hawaii island.

It is the third month in a row that Oahu electric bills have risen. The combined increase for that period is $7.90, which includes $4.89 that was assessed in June as part of the company’s "decoupling" tariff. The tariff, which began in 2011, is received annually by the utility to compensate it for declining sales as more customers use alternative energy sources.

"Fuel costs, which currently make up more than 70 percent of the monthly electric rate, are largely the driver for the fluctuation from last month," HECO spokeswoman Lynne Unemori said. "We know how difficult high bills are for our customers. That’s why we are so focused on cutting fuel costs through the use of cleaner, lower cost renewable energy and alternatives to expensive oil like liquefied natural gas."

HECO, which doesn’t make any profit on fuel purchases, said in June that it has no plans to file for additional rate increases over the next three years beyond what it is getting annually through the decoupling tariff.

The company said it expects to file its next rate case in 2017, adding the caveat that "if circumstances change, a rate case may be filed earlier."

"We were able to do this (rate case suspension) because our utilities are aggressively focused on managing costs by pursuing operational and financial efficiencies," Connie Lau, president and chief executive officer of HECO parent Hawaiian Electric Industries Inc., said on an earnings conference call earlier this month.

On Oahu the August rate rose to 34.9 cents per kilowatt-hour from 34.7 cents a kilowatt-hour in July, when the typical bill was $217.24.

Hawaiian Electric Co., its sister utilities in Hawaii and Maui counties, and the Kauai Island Utility Cooperative adjust their rates monthly to reflect changes in their fuel costs and the prices they pay for electricity purchased from independent power producers.

Hawaiian Electric Cos. has more than 450,000 residential and commercial customers, with 300,000 on Oahu, 70,000 on Maui and 80,000 on Hawaii island. KIUC is a member-owned cooperative that serves 33,000 customers.

The price of electricity in Hawaii is more than three times the national average in large part because of the high cost of fuel oil used for power generation.

Hawaii residents paid an average of 38.0 cents a kilowatt-hour for electricity in May compared with the national average of 12.8 cents a kilowatt-hour, according to the latest data available from the U.S. Energy Information Administration.