U.S. airlines spent $6.66 billion on jet fuel in May, the second straight month that fuel costs topped $6 billion, according to government data released Tuesday.

The May figure was 84% ​​higher than the previous year. Airlines spent $6.47 billion on fuel in April, the Bureau of Transportation Statistics said.

The higher year-over-year spending has been primarily due to the rising price of jet fuel, rather than a significant increase in the amount consumed by airlines. U.S. shippers used 1.627 million gallons in May, down 0.6% from May 2025. Consumption was also slightly lower in April compared to a year ago.

The average price airlines paid for fuel in May was $4.09 per gallon, slightly below the $4.11 in April but 85% higher than the $2.21 they paid in May 2025, the agency said.

Airlines around the world have responded to rising fuel costs by raising fares and cutting flight schedules. Fuel is typically one of the industry’s largest operating costs, leaving shippers particularly vulnerable to swings in energy prices.

The latest figures show the continued impact of sharply rising energy costs after conflict in the Middle East began this year and disrupted shipping through the Strait of Hormuz, a key route for global crude and fuel supplies.

Fuel prices have fallen from their spring highs since the United States and Iran reached an interim ceasefire agreement, offering some relief to airlines after a costly spring. But the truce remains fragile.

Three oil tankers were hit by shells on Tuesday in the Strait of Hormuz, according to the British military, and the United States revoked a license that had allowed sales of Iranian oil under the deal.

Delta Air Lines will report its second-quarter financial results on Friday, kicking off a wave of earnings reports from U.S. airlines. Executives are expected to discuss how recent drops in fuel prices could affect the industry’s finances in the future.

The average price of a gallon of jet fuel on Monday in Chicago, Houston, Los Angeles and New York was $2.90, according to the Argus US Jet Fuel Index, which tracks average daily prices in those key hubs.