Abstract We study experimentally the properties of the majority run-off system and compare them to those of plurality rule. Our focus is on Duverger’s famous prediction that the plurality rule leads to higher co-ordination of votes on a limited number of candidates than the majority run-off rule. We find strong co-ordination forces under both systems. However, as predicted by the theory, in some cases these forces are stronger under plurality. Despite these differences in voting behaviour, we find small and mostly not significant differences in electoral outcomes and, hence, voters’ welfare.