Sales at AutoNation, the nation's largest dealership group, offer a window into the growth of millennial buyers.
AutoNation found millennials, as a percentage of its new-vehicle sales, grew from 9 percent in 2010 to 22 percent through the third quarter last year. Millennial sales during that period grew by at least 25 percent annually.
"It is a changed generation. It is very valuable," said Marc Cannon, AutoNation's chief marketing officer.
AutoNation said in an email response to questions that in 2011, the retail giant first noticed a "year-over-year double-digit increase in millennial sales."
"Millennial vehicle sales have continued to outpace nonmillennial sales for the past six years," AutoNation said.
In a list of most popular models sold to millennials through the third quarter of 2016 by AutoNation, Mercedes-Benz was the only premium brand, and it ranked 12th with the C-class sedan.
Geographically, the biggest increases in millennial sales were in Seattle, most of California, southern Florida and Orlando and Dallas and Austin, Texas.