In cross-cultural business negotiation, culture is known to influence negotiation processes. As a lens to study this effect we deployed the Lemon Car Game, an online negotiation game developed for this purpose (Hofstede et al. in: Proceedings of 39th international simulation and gaming association conference (ISAGA). Technologia, Kaunas, pp 39–46, 2009a; Hofstede et al. in: David, Sichman (eds) Multi-agent-based simulation IX, international workshop, MABS 2008, revised selected papers, LNAI 5269. Springer, Berlin, pp 1–16, 2009b). In this article we report the results from the game, obtained from over 800 players from more than 70 countries. We employ several complementary analyses in a mixed-methods approach. Our findings show that to make sense of the players’ actions during negotiation, economic rationality falls short. A pan-cultural individual-level analysis of actions and stated intentions also fails to yield a coherent picture. Within countries, however, actions and intentions do cohere, as shown by an ecological country-level factor analysis, from which three factors emerge for the sellers at country level: trustworthiness, opportunism, and fairness. We conclude from these findings that, in this game, players are driven by what we call relational rationality: they are rational from the perspective of the social world in which they live, with interpersonal relationships weighing heavily. Relational rationality changes players’ perspective of economic rationality, and thus their observed behaviour in negotiation. Based on this evidence, we extrapolate that relational rationality significantly influences negotiation processes in all cultures.@en