The study found that compliance with underage alcohol sales laws by licensed retail establishments might affect underage alcohol use indirectly through its effect on underage use of commercial alcohol sources and perceived ease of obtaining alcoholic beverages; however, the use of social alcohol sources was more strongly related to underage drinking than use of commercial alcohol sources and perceived ease of obtaining alcoholic beverages. There was a strong positive association between the use of social alcohol sources and past-30-day drinking behaviors. The findings suggest that reducing the availability of direct underage alcoholic-beverage purchases from retail outlets may have only a modest effect on underage drinking. Social sources of alcoholic beverages are apparently much more important than commercial sources. Research on the effects of strategies to reduce social sources of drinking for underage youth is limited. In 2005, alcohol-beverage purchase surveys were conducted at 403 off-premise licensed retail establishments in 43 Oregon school districts. A survey was also administered to 3,332 11th graders in these districts. Multilevel logistic regression analyses were used to examine relationships between the school district alcohol sales rate and students' use of commercial and social alcohol sources, perceived ease of obtaining alcohol, past-30-day alcohol use, and heavy drinking. 3 tables, 1 figure, and 16 references