Both Norway and England have used the supplementary vote (SV) method to elect mayors. SV was intended to elect mayors with a broad popular mandate, and deemed easy for voters to use. Previous research on English mayoral elections focusing on the supply side of the elections has found that voters supporting minority candidates with their first vote face difficulties using the optional second vote to choose among the remaining two top-candidates in municipalities where there are many candidates in the race. A close race, on the other hand, seems to give voters a helping hand in making this choice. Drawing on these findings, we link data on the 48 Norwegian mayoral races to survey data to further explore how the supply side of the elections and individual voter resources affect effective voting and use of the optional second vote. We use both standard logistic regression and multi-level models as statistical tools. The result reveals that 27 out the 48 elected mayors in Norway came out as majority winners (more than 50 per cent of the votes). The analysis suggests that the supply side of the elections is of minor importance for whether voters use their second vote or not. The probability of using the second vote is reduced by age, and voters who claim to understand how the electoral system works use the second vote more frequently. The analysis also reveals considerable variation in the number of first and second votes for the top two candidates (effective votes) between municipalities, and the results suggest that this variability may be explained partly by the closeness of the elections. Voters in municipalities with competitive mayoral races are more likely to vote effectively than voters in municipalities with less competitive elections. At the individual level party members are more likely to vote ineffectively