On a steamy evening at Flushing Meadows Corona Park in Queens, Jaime Cabal had a line of customers at his Mister Softee ice cream truck. He blended milkshakes, topped bowls of vanilla soft-serve with strawberries and dipped cones into cherry and blue-raspberry shell. One boy no sooner finished his treat than he begged his parents for more, pointing at the menu’s pops shaped like SpongeBob SquarePants, Sonic the Hedgehog and Tweety.

Crowds like these are becoming rarer for ice cream vendors across the country as high fuel prices feed inflation, leaving some owners of soft-serve trucks questioning their future in the business.

Owning an ice cream truck used to be a lucrative proposition, but for some, the expenses have become untenable: The diesel that powers the trucks has topped $7 a gallon, vanilla ice cream costs $13 a gallon and a 25-pound box of sprinkles now goes for about $60, double what it cost a year ago.

Many vendors say the end of the ice-cream-truck era has been years in the making. Even the garages that house these trucks are evolving, renting parking spaces to other types of food vendors as the ranks of ice cream trucks dwindle.

Parks, pools and residential streets used to be prime territory for the ice cream man. But now, more often than not, a soft-serve truck’s jingle plays to a crowd of no one as prices for some cones with add-ons like swirly ice cream and chocolate sauce reach $8 on some trucks.

Though no organization appears to have hard figures on just how many ice-cream trucks are currently working the streets of New York City, some owners said they would likely leave the business in the next few years. It’s a sentiment that is felt nationwide, where mobile ice-cream vendors face higher costs for city permits and registration, and hefty competition from other ice cream businesses, said Steve Christensen, the executive director of the North American Ice Cream Association.

The ice cream truck, he said, is “unfortunately becoming a thing of the past.”

New delivery methods, through third-party apps or ghost kitchens, are proliferating. Brick-and-mortar scoop shops are focusing on offering a fun experience, he said, and serve dozens more flavors than a traditional ice cream truck can, driving lines away from these vehicles.

“It’s horrible,” said Mr. Cabal, the ice cream vendor in Queens, who has worked on ice cream trucks for the last nine years. Inflation has even raised the cost of mechanical parts for the truck. Last year, when his slushy machine broke down, a part he needed cost $1,600. He decided to wait a few more months to fix it, but the part nearly doubled in cost, to $3,000. Now, the slushy is off the menu and the machine is sitting in his garage.

In 2018, Mr. Cabal thought business in the Flushing Meadows Corona Park would be good enough to support his own truck, so he sold his house in New Jersey for $380,000, moved to Hicksville, N.Y., and bought a Mister Softee franchise. He won a contract with the city to operate in the park.

Despite the tens of thousands of dollars he pays each year for that permit and others, Mr. Cabal has contended with unlicensed vendors who sell fruit, empanadas and Duro wheels from baby strollers, and even ice cream from pushcarts strategically placed around his truck. He said they undercut him on price so much that it’s impossible for him to compete.

In Lower Manhattan, Ramon Pacheco is struggling with his recent decision to raise his prices by 50 cents to account for some of his increased daily expenses, like $80 in gasoline ($15 before the pandemic) and $40 in diesel, ($18 earlier). He now pays about $41 for the three gallons of vanilla ice cream that used to cost him $27.

He has sold ice cream for 27 years, and since the pandemic, he said he’s noticed a drop-off in demand. He now takes in as little as $200, before expenses, selling ice cream for nine hours. Sometimes, if a regular customer comes to him with $2 for ice cream, he’ll just sell it at a loss.

“I’m 66, and I’m tired,” Mr. Pacheco said in Spanish, adding that he is thinking of selling his truck next year.

Carlos Cutz decided to leave his job at a deli two years ago to work on an ice cream truck to support himself, his wife and their three children. He took out a loan and bought his own truck in May.

The ice cream man he bought it from had a route in Williamsburg, Brooklyn, and Mr. Cutz has resisted raising the prices to avoid alienating his customer base, even though his expenses have doubled for products like a package of 250 cake cones.

“These have been the worst years for ice cream trucks,” he said in Spanish, adding “I’m going to try to do the best that I can to continue with this business. I’m feeding my family, and I can’t leave a business I haven’t tried.”

The price of gasoline has been the most shocking expense in recent months for Andrew Miscioscia, the owner of Andy’s Italian Ices NYC which operates three trucks for private catering events. He spent $6,800 in June on gas alone. Mr. Miscioscia pivoted to catering during the pandemic when sales slipped on the Upper West Side.

“People are not getting out like they used to,” he said. “And there’s a lot of competition out there.”

Still, the appearance of an ice cream truck on a hot summer day remains a thrill for many. At Flushing Meadows Corona Park, Domenica Chumbi, of Hillside, N.J., held a vanilla cone dipped in cherry shell for her quinceañera photos. The pink-hued ice cream not only matched her dress and her party’s theme of cherry blossoms, but it also summoned memories of childhood visits to the park.

“It’s something that reminds me of New York,” she said.