Alcohol use is a persisting social and health problem in Spain that often takes place within the recreational context. This study aims to analyze objective and self-reported measures of alcohol use and to assess the potential role of social factors on alcohol intake in open-air public settings. A total of 1475 participants (47.4% women), including 27.8% adolescents organized into 355 natural groups of friends, were interviewed while they were socializing at night in the streets of Palma (Spain). Breath alcohol concentration (BrAC), self-reported measures of alcohol use, and social variables were assessed. Men showed statistically higher scores in BrAC than women. However, adolescents’ Alcohol Use Disorders Identification Test (AUDIT) scores were not statistically different by gender. Correlation between objective and self-reported measures was low. Interestingly, BrAC of drinkers was lower when some friends in the group were sober. Moreover, especially in young adults, variables related to the social environment were statistically significant factors to predict BrAC. In conclusion, we found a high prevalence of alcohol intake in young people in open-air public settings, low relationship of objective and self-reported measures, and social factors linked to alcohol use, although differences by age and gender must be considered.