Young adults typically drink socially, yet most lab studies testing alcohol responses have administered alcohol in isolation. This is the first study to examine alcohol responses and social reward in a group setting among a young adult at-risk sample. Heavy drinking young adults (=393; 50% female) were grouped in threes and drank a moderate dose of alcohol or a placebo. These social interactions were recorded, and the duration and sequence of facial expressions, speech, and laughter were coded. Results revealed a comprehensive, multimodal, positive effect of alcohol on socioemotional experiences across self-report (e.g., increased positive affect and social bonding, greater relief of unpleasant feelings) and behavioral outcomes at both the individual- (e.g., more rapid increases in Duchenne smiling) and group-levels (e.g., more three-way conversations). Findings underscore the potential for group-formation paradigms to yield valuable data regarding etiological mechanisms underlying alcohol use disorder. All data and code are available (https://osf.io/3q42z/).