This paper presents the first sociolinguistic examination of communication in social dilemmas. 90 participants (18 groups of 5) completed a modified public goods game with 2 rounds: an effort-based task and an unscripted online chat about the results. A linear regression shows that consensus-building language in the Round 1 chat affects cooperative behaviour in the Round 2 task. A qualitative analysis of 3 groups explored how participants use different recognisable styles of communication (registers), to strategically align with or disalign from one another (stancetaking). Each analysis is complemented with a quantitative visualisation of how (dis)alignment between participants unfolds in real-time. We found that successful groups employ registers associated with collective action, such as gameshow talk (“ouch. £69 out of a possible £120”), to encourage, punish, and pledge allegiance to one another. Less successful groups use registers that risk evoking mistrust and reducing obligation, such as business talk (“I approve”). We argue that a mixed methods approach to interaction and behaviour can reveal incremental shifts in consensus building that underpin quantitative outcomes.