Booking trips on a mobile device is becoming more and more common, a new survey shows. The survey showed that 18 percent of American adults who have ever booked travel, have done so using a mobile device.

The  American Travel Behavior Survey, which was conducted online in October 2013 on behalf of Hotwire by Harris Interactive among over 2,000 U.S. adults ages 18 and older, also found that younger adults are significantly more likely to book travel on mobile devices. The survey showed that 37 percent of adults ages 18-34 and 25 percent of adults ages 35-44 used mobile devices to book a trip.

Of the respondents, 12 percent said they booked their trip on a smartphone, 10 percent have booked a trip on a tablet device. They were more likely to use a web browser than a travel app.

"Mobile purchasing has become an increasingly large trend in travel, given that more than half of Americans now own smartphones*," said Henrik Kjellberg, president of the Hotwire Group. "So, I see the 18 percent as the tip of the iceberg in terms of mobile travel booking, considering players in the space are continuing to optimize their sites and products for the mobile booker."

Hotwire itself saw a steep increase in mobile bookings. The site experienced a 60 percent year-over-year increase in mobile bookings for the first nine months of 2013. Almost 20 percent of Hotwire transactions occur on a mobile device.

The survey also found that 48 percent of adults said they are more comfortable with eleventh hour booking than they were five years ago. The site found that 80 percent of Hotwire's bookings  on a mobile phone and 70 percent on a tablet are made at the last minute (the day before or day of arrival).

"Mobile is ideal for last-minute travel bookings as many providers offer incredible discounts through easy-to-use travel apps like Hotwire's, especially on bookings made the day of arrival," Kjellberg continued. "We expect the number of mobile bookings to grow exponentially, outpacing desktop bookings in the next year or two, as more people of all ages become comfortable booking through their mobile device and making last-minute purchases."