Hawaii’s largest utility is warning residential customers to brace for a 20% to 30% jump in their electric bills in the coming months. In Alaska, the Golden Valley Electric Association in Fairbanks is also telling customers to get ready to pay more.

The power markets in Hawaii and Alaska are among the first in the U.S. to feel the reverberations of the global energy shock caused by the Iran war.

The U.S. grid has been resilient for the most part because domestically produced natural gas — the country’s main fuel for generating power — is actually cheaper now than it was at the start of the conflict. But there are no natural gas pipelines to Fairbanks or Hawaii.

Petroleum products account for only a sliver of power generation nationally but are of outsize importance in more remote regions. Last year, more than 70% of Hawaii’s large-scale power generation and 16% of Alaska’s came from petroleum liquids, according to the U.S. Energy Information Administration.

Oil prices have soared since the war broke out in late February because about 20% of the world’s oil and gas is trapped behind the Strait of Hormuz. Despite falling over the past two weeks, U.S. crude prices are still up more than 30% since the conflict began.

Even if traffic resumes through the strait, it will likely take several months for the energy trade to normalize. The utilities in Hawaii and many in Alaska, for instance, buy fuel regularly to operate their power plants — but there is a lag before those higher costs get passed through to customers.

Hawaiian Electric has told Oahu residents that they can expect to see higher electricity bills this month, followed by the Big Island and Maui in May and June.

Travis Million, chief executive of Alaska’s Golden Valley, says he isn’t sure exactly what to tell customers to expect, other than that fuel charges likely will be higher starting this summer.

“It’s a tough message to put out there,” he said, noting that Alaska is coming off an exceptionally cold winter that pushed up home heating costs.

Golden Valley has about 50,000 metered connections and serves an area the size of Connecticut. The nonprofit cooperative added 70,000 barrels of fuel storage in December, roughly enough to hold a 30-day supply, but it couldn’t fill the new tanks before the war because the cold winter had already strained refinery supplies, Million said.

The situation became acute in March when prices for diesel and naphtha rose 50%.

“We see those prices change basically on a daily basis, as it’s changing in the world market,” said Million.

Puerto Rico also relies heavily on oil for generating power, but Cathy Kunkel, a consultant with the Institute for Energy Economics and Financial Analysis, said its residents aren’t yet facing the same sticker shock. That is because the territory imports liquefied natural gas under contracts that are more closely tied to U.S. natural gas prices than to those paid by customers in other parts of the world.

Natural gas costs have surged in Asia and Europe, where customers import much of the fuel they use.

Several factors are keeping U.S. natural gas prices in check: ample inventories, record production and capacity to export LNG that, for now, is nearly maxed out. Seasonal factors are also at play. Unlike in Europe, where inventories are unusually low, the U.S. ended the heating season with plenty in storage, giving most of the country a cushion until the start of next winter.

That wasn’t the case in 2022 when Russia invaded Ukraine. Back then, the U.S. was coming off a cold winter with lower-than-normal inventories of natural gas. The invasion sent prices soaring, and power bills spiked across much of the country. Exports to Europe increased.

Natural gas futures for May delivery settled April 20 at $2.69 per million Btu on the New York Mercantile Exchange, down about 6% from the start of the war.

“We’re self-sufficient,” said Eugene Kim, research director for Americas gas at Wood Mackenzie. “The only time that we do connect to global prices is when there is a fear that the U.S. will not have enough gas in storage before the start of winter.”

If the energy market doesn’t normalize in the coming months, New England and other areas could also feel the pinch. Power plants there sometimes switch to oil during periods of extreme cold when natural-gas supplies or electricity imports are constrained. Many homes also rely on oil for heating.

War-related supply disruptions in the Middle East have increased the attractiveness of U.S. gas on the global market. The U.S. exports as LNG about 18% of the gas it produces, predominantly from the U.S. Gulf Coast, and that market is set to grow in the coming years.

For now, higher oil prices are providing a windfall to Alaska’s state budget. That could be good news for Alaskans if politicians opt to increase the annual dividend residents receive from the state’s oil wealth fund. A higher dividend check could help households purchase heating fuel for next winter. Last year, they received $1,000 checks. This year, lawmakers are considering a higher amount.

“We’re integrated in the global economy like everyone else is,” said Brett Watson, associate professor of applied and natural resource economics at the University of Alaska Anchorage. “We experience the pain of that in times like this, but we also experience the benefits.”