However, researchers at the University of Minnesota School of Public Health also found that only 8 percent of the general adult population entering alcohol establishments was willing to purchase the alcohol.

Most underage drinkers obtain alcohol from social sources, individuals who illegally provide alcohol to youths -- parents, parents of friends, friends, acquaintances, co-workers, siblings, and even strangers -- as opposed to commercial sources, according to lead author Traci Toomey.

"Shoulder-tapping" occurs when an underage person approaches a stranger outside of an alcohol establishment and asks the stranger to purchase alcohol for him or her.

The small percent of the general population that agreed to purchase alcohol when approached is encouraging, but one out of every five young males approached bought the alcohol when requested, said Toomey.

The study also found that adults approached at a city convenience or liquor store rather than one located in a suburb were nine times more likely to make the purchase, according to the study published in the July issue of Alcoholism: Clinical & Experimental Research.