Office space in Silicon Valley isn’t the only real estate that’s gotten scarce in the booming technology market. The U.S. organization that distributes some of the Internet’s most important virtual property is running out of inventory.

Some savvy companies have been stocking up, but the shortage could mean headaches—and significant costs—for U.S. businesses looking to expand on the Internet.

The limited supply of new Internet Protocol addresses is nearly gone. Asia essentially ran out in 2011, and Europe a year later. North America’s allotment is due to dry up this summer.

“Enterprises that don’t have a plan for what to do with this will have this brought up by their board,” said James Cowie, chief scientist at Dyn, an Internet consulting firm.

IP addresses are the Internet’s equivalent of telephone numbers. These numerical codes are different from the familiar top-level domain names that end in .com or .org. They are used behind the scenes anytime data moves over the Net—when a laptop requests a Web page, a smartphone posts an Instagram photo or a Nest thermostat downloads a software update.