SANTA MONICA, Calif. — American auto brands are gaining strength with younger buyers in the U.S. market, while their Japanese rivals have taken a big step back, reports vehicle information site Edmunds.com.

According to an analysis of new-car retail registrations from R. L. Polk & Co., American brands accounted for 36.8 percent of cars bought by Americans age 25 to 34 in 2012, up from a share of 35.4 percent in 2008. Meanwhile, the share of Japanese brands for the same age group plummeted from 50.6 percent to 42.9 percent during that period.

But even with the incremental success of American brands, Edmunds.com found that the exodus from Japanese cars by young buyers is turning mostly toward South Korean brands. About 10 percent of new cars purchased by 25 to 34 year olds in 2012 carried South Korean nameplates, more than doubling the rate for this age group since 2008.

"U.S. automakers have burst onto the scene in recent years with small, fuel-efficient and affordable cars that really appeal to a young set of buyers," says Edmunds.com Sr. Analyst Jessica Caldwell. "But while Detroit might be chiseling away at the Japanese grip on Gen X and Gen Y, South Korean brands are taking big hacks. Not only are the Koreans making better cars for young people, but they've also worked to make credit available to young buyers who still don't have solid credit history."

Retail Registrations by Age, 2012 vs. 2008

Source: R.L. Polk & Co.

The South Koreans' progress with young buyers reflects their overall growth in the U.S. market, the vehicle information site said. Korean brands represented 9.5 percent of all new retail registrations in the U.S. in 2012, almost twice as much as their share of 5 percent in 2008.

European car labels are flexing their own muscles in the U.S. market as well, accounting for 9.9 percent of new-car registrations in the U.S. market last year, up from 8.5 percent in 2008. Like the South Koreans, European carmakers have delivered consistent growth among all age groups since 2008, with the biggest successes among older car buyers, thanks to Baby Boomers choosing European luxury cars post-retirement.