"Among all underage current drinkers, 31.0 percent paid for the alcohol the last time they drank, including 9.3 percent who purchased the alcohol themselves and 21.6 percent who gave money to someone else to purchase it. Underage persons who paid for alcohol themselves consumed more drinks on their last drinking occasion (average of 5.9 drinks) than did those who did not pay for the alcohol themselves (average of 3.9 drinks).
"More than one in four underage drinkers (25.8 percent) indicated that on their last drinking occasion they were given alcohol for free by an unrelated person aged 21 or older. One in sixteen (6.4 percent) got the alcohol from a parent or guardian, 8.3 percent got it from another family member aged 21 or older, and 3.9 percent took it from their own home."
Pemberton, M. R., Colliver, J. D., Robbins, T. M., & Gfroerer, J. C. (2008). Underage alcohol use: Findings from the 2002-2006 National Surveys on Drug Use and Health (DHHS Publication No. SMA 08-4333, Analytic Series A-30). Rockville, MD: Substance Abuse and Mental Health Services Administration, Office of Applied Studies.