Most underage drinkers get their alcohol from "social sources" -- people who buy them alcohol -- and a new study finds that young males are the most likely group to purchase alcohol on behalf of young drinkers.

Researcher Traci Toomey and colleagues at the University of Minnesota Prevention Research Center reported that young males are the most likely to go along with "shoulder tap" requests to buy alcohol for high-school students. Researchers randomly selected 219 alcohol outlets and sent underage-looking requesters to ask people outside the stores if they would purchase a six-pack of beer for them. They found that 8 percent of all adults agreed to make the purchase, but that 19 percent of young males (estimated ages 21-30) went along with the request.

"Although 19 percent may sound like a relatively low success rate, it means that a given youth has about an 80 percent probability of obtaining alcohol within eight attempts with randomly selected adults," said Toomey. "The actual success rate is probably higher because youth are most likely selective in who they approach and where."

Researchers suggested that young adult males should be targeted with prevention messages and warnings about providing alcohol to underage youth.

The study appears in the July 2007 issue of the journal Alcoholism: Clinical and Experimental Research.