If you’ve already made plans to go away this summer, you probably have a sense of just how many options there are for booking a trip. Most often, finding a good deal requires little more than sitting down at a computer.

Websites like Expedia, ORBITZ, and Kayak have been reshaping the world of travel for years, offering consumers discounts on places to stay and airfare to get there. With Expedia’s positive earnings call at the beginning of the month, it’s likely these kinds of sites won’t be going anywhere soon.

Still, after surveying about 2,500 adults on their experiences when booking flights for a trip, CivicScience found that clear skies now don’t negate the possibility of turbulence in the future. Below are the results for those respondents that fly.

For starters, going directly through an airline is still the most popular method of booking airfare for people who fly somewhat regularly. Discount travel sites like Expedia aren’t terribly far behind, of course, and are well above alternatives like traditional travel agencies.

These sites also remain popular options for adults between the ages of 25 and 54, with Millennials a bit more likely to use them than Gen Xers. The bad side? They don’t hold the same appeal for adults under 25. Only 22% of Gen Zers book airfare through discount travel sites, while 62% prefer to go directly through the airlines.

It’s difficult to say why these sites haven’t been more popular with Gen Z. Airline-rewards credit cards are certainly the most popular with this group, but not by much. They could explain part, but certainly not all, of the reason adults under 25 lean heavily toward booking flights directly with an airline.

The disparity in age might also have something to do with the amount of time people can devote to planning a trip. In general, the longer someone takes to plan a vacation, the less likely they are to book directly through an airline.  Adults who plan for six or more months are nine times more likely to go through a travel agency than people who plan vacations and travel quickly. 

Interestingly, parents who travel are less likely to use these sites. Only 27% of parents end up booking flights through a site like Expedia, compared to 37% of non-parents. Grandparents, who rely far more on traditional travel agencies than anyone else, also use discount sites more often than parents, and at almost the same rate as non-parents.

Sites like Expedia may have a leg up on the airlines when it comes to flying in groups, though. Adults who are most confident traveling by themselves tend to bypass discount sites and book straight through an airline. But as confidence in solo travel dips, dependence on these websites goes up. Whereas 34% of adults who are okay with traveling alone rely on discount sites to book flights, 51% of adults who aren’t at all comfortable traveling solo do so.

In the end, discount travel sites are still doing well, especially with Gen Xers and Millennials. Numbers for the latter could take a hit as more Millennials become parents, but Gen Xers may provide some counterbalance as they near retirement and start having more time to travel. Ultimately, it’s Gen Z who pose the biggest hurdle. In order to keep pace with the airlines, discount travel sites will need to get this group on board—more of whom are entering the workforce and accumulating the means to travel.