Orbitz Worldwide Inc. has found that people who use Apple Inc.'s Mac computers spend as much as 30% more a night on hotels, so the online travel agency is starting to show them different, and sometimes costlier, travel options than Windows visitors see.

The Orbitz effort, which is in its early stages, demonstrates how tracking people's online activities can use even seemingly innocuous information—in this case, the fact that customers are visiting Orbitz.com from a Mac—to start predicting their tastes and spending habits.

Orbitz executives confirmed that the company is experimenting with showing different hotel offers to Mac and PC visitors, but said the company isn't showing the same room to different users at different prices. They also pointed out that users can opt to rank results by price.

Orbitz found Mac users on average spend $20 to $30 more a night on hotels than their PC counterparts, a significant margin given the site's average nightly hotel booking is around $100, chief scientist Wai Gen Yee said. Mac users are 40% more likely to book a four- or five-star hotel than PC users, Mr. Yee said, and when Mac and PC users book the same hotel, Mac users tend to stay in more expensive rooms.

"We had the intuition, and we were able to confirm it based on the data," Orbitz Chief Technology Officer Roger Liew said.