American Airlines Group Inc. and Southwest Airlines Co. are carrying extra jet fuel on some flights and considering adding stops to other routes to pick up fuel as snarls in U.S. trucking and supply chains delay deliveries to small and mid-sized airports across the country.

The delays are expected to continue through mid-August, American told its pilots in a memo Monday. Aviators were told to use all conservation measures when possible and cautioned that carrying added fuel will result in heavier aircraft when landing.

“Station jet fuel delivery delays can occur in all regions of the U.S. and will affect all airlines,” said the note to American’s pilots.

This is the latest example of disrupted fuel supplies because of trucking woes. While the whole country has plenty of gasoline and even a glut of jet fuel, truck drivers who distribute supplies have been hard to come by just as travel demand comes roaring back. That’s left some far-flung filling stations at least briefly without fuel in states from Florida to Iowa to Oregon and has now sparked the warnings from airlines.

For jet fuel, U.S. stockpiles stand at their highest seasonal level in a decade. That’s partly because oil refiners are trying to cash in on resurgent gasoline demand by raising production rates, which indirectly leads to more jet fuel output. Shortages of transportation equipment, drivers and pipeline-space allocation are being blamed for the supply-distribution problems.

“The larger issue here is that jet fuel has lost pipeline space to gasoline and diesel over the past year due to the pandemic,” Delta Air Lines Inc. said in a statement. “The Federal Energy Regulatory Commission, the pipelines, and the airlines need to work together to allow space on the pipelines to ship the needed jet fuel to the airports.”

The delays have had minimal effect on flights by American and Southwest, while Delta said its operations haven’t been affected. United Airlines Holdings Inc. referred questions to Airlines for America, the trade group for the largest U.S. carriers.

Airlines for America is "in communication with federal authorities and pipeline operators to address this jet fuel capacity issue," the group said in a statement.