Imagine scrolling through your phone while you’re en route to a bar, and seeing an ad for Grey Goose vodka, or pulling up to the airport and seeing a coupon for Auntie Anne’s. A new advertising program from Uber will soon make that a real possibility, allowing major brands and smaller advertisers to target consumers on mobile devices based on where they have been and where they are going in real time.

The program is called Journey Ads, and it’s quite possibly the biggest topic being discussed among brand marketers this week.

With Journey Ads, advertisers will be able to sponsor Uber trips and target riders based on their destinations. The ads themselves show up in Uber’s mobile app as part of the company’s new media division. Riders will be able to click to buy advertised products without leaving the Uber app.

While major brands will likely be the first to try Journey Ads, the ad-targeting product will eventually become available to businesses of all sizes, including SMBs. When that happens, businesses will be able to place ads using data coming from riders’ recent travel histories and their geographic ride destinations in real time. If a rider orders an Uber ride to a specific restaurant or airport, a business could buy ads based on that location. So, for example, a quick-service restaurant located at the airport could buy an ad that would appear on the rider’s mobile phone while they’re en route. In a certain scenario, the business might even use limited-time discounts or other targeted promotions to encourage riders to give them a try.

Individual brands would also be able to sponsor certain trips. In that case, the only ads the rider would see in the Uber mobile app would be coming from one specific brand, from the time they first order the Uber until they arrive at the destination. Uber is calling these ads “journey ads,” and they’re expected to be sold on a per-trip basis.

Ads sold through the Journey Ads program are made up of three distinct timeframes — while the rider is waiting for a car, while they’re in a car, and when they arrive at their destination.

Journey Ads will likely be different from most digital ad programs. Rather than charging businesses based on impressions or click-throughs, Uber is charging based on the trip.

“We spend eight hours a week in a car; it’s a huge advertising opportunity,” explained Mark Grether, general manager of Uber Advertising, in an interview with the Wall Street Journal.

Although Uber has been selling ads for years, most of those ads have previously been in the form of sponsored listings on Uber Eats, Uber’s food delivery service. Journey Ads marks the company’s biggest step yet into the mobile ad space.

Uber expects its expanded advertising business to reach $1 billion in revenue by next year. In interviews, the company’s executives have said they believe the opportunity for ride-hail advertising could be substantially more lucrative than food delivery. The company is also piloting in-car tablets, which would presumably host advertising in the future, as well.

Uber isn’t the only ride-sharing company jumping into the mobile ad market. Lyft launched its own advertising unit—Lyft Media— back in August. Around that same time, the rideshare company also started adding tablets that riders can interact with in some Lyft cars.

While consumer privacy will almost certainly become an issue here, Journey Ads are presenting marketers with an incredible opportunity. With geolocation data from the company, sophisticated brand marketers will essentially be able to unravel people’s lives to understand not just where they are going, but also why they are going there.

Uber has access to a trove of personal data about its users, including home addresses, credit card numbers, and places they visit. The company has said it will not share that individual user data with advertisers, but there are questions about how data gets aggregated and where the line gets drawn when it comes to targeting ads on the Uber app. This is one issue we’re likely to see coming up more frequently over the next few months.