Every season now seems like peak season for Leonard Wright, who’s constantly recruiting drivers to staff his INPAX Shipping Solutions. The relentless growth of Amazon.com’s Prime memberships has led the e-commerce giant to tap courier services like INPAX to make same-day and two-day deliveries in what’s called “the final mile” to customer homes.

“In the final-mile world, there’s more work than you can handle,” said Wright, who employs 300 drivers running U.S. routes for Amazon and 200 independent contractors for non-Amazon accounts. Atlanta-based INPAX and other regional services supplement the major haulers – United Parcel Service, FedEx and the U.S. Postal Service.

The rush to bring everything from groceries to gourmet meals to customers’ doorsteps has sparked such a demand that job postings for delivery drivers have tripled nationwide on Indeed.com in the past three years. The dearth of truck drivers needed to carry products from city to city is well documented, but the growth of e-commerce depends as much or more on a steady supply of qualified last-mile car and van drivers.

Despite concerns, the forces propelling the demand for more delivery drivers show no sign of slowing. Amazon said in April that its Prime memberships had topped 100 million. Grubhub, meanwhile, works with more than 80,000 restaurants in 110 U.S. markets, up 38 percent in the first quarter of this year from the end of 2017, company filings show.

“There are going to be challenges in hiring,” said John Haber of the logistics consultancy Spend Management Experts. “If you follow what’s happening in the truckload market, people cannot find drivers. There are trucking assets that are sitting unused, because they can’t find people to drive the trucks – and those are for high-paid employee positions.”

With supermarkets set to move more heavily into food delivery, competition for drivers will ramp up further, said Antony Karabus of HRC Retail Advisory. Keeping raw chicken and milk from spoiling means they’ll need more training than most delivery people.

“You’re not going to have enough drivers who are capable,” Karabus said. “Just getting a warm body to drive is not enough.”

Too many food delivery companies are chasing too little business, and several will be forced to consolidate to survive, Karabus said. In the package business, venture-capital backed shipping company Shyp shut down in March after realizing too late that it needed to focus on business shipments rather than consumer ones.