An archival analysis of evaluations of wines provides a unique context in which to investigate social influence in a naturalistic setting. We conducted analyses based on 6,157 notes about 106 wines posted by wine drinkers at a wine social networking site. Our findings suggest that social influence on private wine evaluations occurred by communicating a descriptive norm via written information. We provide empirical evidence that there is social influence on private wine evaluations that is greater than the effect of experts’ ratings and prices combined. This influence comes mainly from the first few group members, and increases as a function of source uniformity. Together with a lack of evidence that more credible or expert members have more influence, these findings suggest that influence in this setting is normative rather than informational. Results have implications for widespread effects of social influence on consumer and other websites where we are subject to the power of others’ opinions.