American gas-station owners are facing a tough decision over whether to invest in electric-vehicle charging stations, a costly bet that currently makes little financial sense but might help future-proof their businesses.

Some gas stations, convenience stores and truck stops are adding chargers to test the technology and protect their market share for the long run. Others say they crunched the numbers and decided they can’t justify the cost, given the small share of electric-vehicle drivers. Charging units and installation typically cost upward of $100,000 each, and might entail the expense of tearing up pavement to lay conduit.

Auto makers including General Motors Co. and Ford Motor Co. are aggressively expanding their lineups of electric vehicles, and President Biden last week set a target to increase U.S. sales of electric, plug-in hybrid and hydrogen fuel-cell vehicles to 50% by 2030. However, electric vehicles made up only about 2% of new U.S. sales last year, and 3% in recent months.

Electric-vehicle entrepreneurs are working on the industry’s biggest bottleneck: charging infrastructure. Companies are building more chargers, but it may not be enough to make EVs work for people who can’t plug in at home. Photo illustration: Carlos Waters/WSJ The Wall Street Journal Interactive Edition

“We don’t see an investable marketplace,” said A.J. Siccardi, president of Metroplex Energy Inc., the fuel-supply subsidiary of RaceTrac Petroleum Inc., which owns more than 750 RaceTrac and RaceWay gas stations, primarily in the Southeastern U.S. “We’re perfectly OK putting capital at risk. The key is we’ve got to have a viable business case,” he added.

Metroplex has been evaluating electric-vehicle charging for about two years and would like to invest but so far hasn’t found a deal that makes sense, Mr. Siccardi said, noting that risks include potential competition with utilities, some of which have their own plans to build charging stations.

Retailers say they are “fuel agnostic” and want to sell anything customers want, but when to add chargers is a subject of debate within companies. Most electric-vehicle drivers can plug in at home, while places like shopping centers are adding chargers that can power a battery over a period of hours.

A customer fuels up with gas at High Country Market Bistro and GastroPub in Round Rock, Texas. Its owner says there is little demand for electric charging.

America’s 150,000 convenience stores, about 121,000 of which offer fueling, are considered the most likely retailers to deliver a powerful dose of electricity—known as a fast charge—to boost a battery in about a half-hour. And they can potentially profit from selling snacks, cigarettes and other higher-margin products while drivers wait.

Industry groups representing convenience stores, fuel retailers, restaurants and others lobbied in recent weeks to strike provisions from the $1 trillion infrastructure bill to allow charging at highway rest areas. The pull-offs, which for decades have banned commercial activity, are seen as spots where utilities might build chargers.

Pilot Co. operates more than 900 retail and fueling locations in the U.S. and Canada. Its chief executive, Shameek Konar, said even the most popular of the company’s 58 chargers are in use only about 5% of the time, whereas they would have to be in use about 30% of the time to earn a return.

“The economic case today for EV charging investment does not exist,” he said, adding that policies are needed to encourage private investment and public-private partnerships.

The owner of High Country Market Bistro says adding chargers would mean less parking space for customers who dash in and out.

Companies investing in charging describe it as something of an experiment. TXB Stores, an Austin-based chain that has 46 gas stations in Texas and Oklahoma, will open its first with charging stations this month.

“We’re going to put them in. Maybe it’s backwards, but then we’ll figure it out,” Chief Executive Kevin Smartt said he told his staff.

Unlike with liquid fuels, which are purchased and marked up for sale to customers, Mr. Smartt said he will have to estimate the right price for selling electricity. Fees levied for brief spikes in power use during fast charging might raise the company’s utility bills in unpredictable ways, he said.

“We’re just totally guessing at what that fee is and what it will take to cover our total costs,” Mr. Smartt said. “We’re going to have to look at it on a month-by-month basis and kind of go back and see if we’re close.”

Peak demand charges are a challenge to solve, said Michael Farkas, chief executive of charging equipment and network provider Blink Charging Co. Utilities must build infrastructure to deliver electricity to multiple cars fast charging at once; in addition, fast charges can degrade wiring more quickly than steady electricity use.

Zahir Walji owns and operates High Country Market Bistro and GastroPub in Round Rock, Texas, a gas station and store with a bar offering specialty wine. He said adding chargers would require a costly redesign or take parking spaces from customers who dash in and out of the store.

High Country Market Bistro owner Zahir Walji prepared last week for a wine class he gives at the store.

“I have not gotten enough customers even saying, ‘Hey, did you ever think about this?’” Mr. Walji said.

Other business operators also doubt their customers will switch to electric vehicles soon. Murphy USA, which has more than 1,650 locations, acquired QuickChek Corp. in February, a deal that included 157 stores in the Northeast, some of which accommodate electric vehicles. But its latest survey of customers showed that most drive a 12-year-old car or truck that cost less than $15,000.

“Electric vehicles have to be affordable, which they aren’t,” Murphy CEO R. Andrew Clyde said. “I’m not a denier,” he said, acknowledging that electric vehicles are poised for growth; but he sees a long adoption period and plenty of runway for selling gasoline and diesel.

Electrification of cars, trucks and buses is a long-term threat to the entire oil market, said Pavel Molchanov, energy analyst with Raymond James. But with low adoption, U.S. companies feel less urgency than their European counterparts to invest in charging.

Government funding is the only way to resolve a shortage of chargers in the middle of the country and create a network to mollify electric-vehicle drivers who worry they might not find a station in time to recharge, Mr. Molchanov said.

“What really drives us to put locations in is when there’s heavy subsidies available, where we can more or less build it for free,” said J.P. Fjeld-Hansen, vice president of Trillium, the alternative and renewable fuels subsidiary of Love’s Travel Stops & Country Stores Inc., which has more than 560 locations.

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Its electric-vehicle chargers aren’t heavily used, Mr. Fjeld-Hansen said, but the company views them as part of an energy transition strategy that includes offering compressed natural gas, renewable natural gas, renewable diesel or hydrogen for customers trying to hit sustainability targets.

Some of those who have put money into chargers say they see it as a way to keep well-heeled customers who are going electric. Lonnie McQuirter, owner of the 36 Lyn Refuel Station in Minneapolis, installed a fast charger in 2014, thinking of it as a way to differentiate his store, along with offering local and organic foods.

“If someone has a disposable income,” Mr. McQuirter said, “it might be the person that can afford a Tesla.”

Write to Jennifer Hiller at jennifer.hiller@wsj.com