The purpose of this paper is to test forward-looking incentives against backward-looking incentives. Design/methodology/approach ? Wage growth model to estimate forward-looking effects of unpaid overtime and a probit model of participation in unpaid overtime controlling for excessive pay to estimate backward-looking effects. The authors use data form the OSA labour supply panel (years 1994, 1996 and 1998). Findings ? The importance of backward-looking incentives is demonstrated in an empirical analysis of participation in unpaid overtime. The authors show that employees who have relatively good wages now or who have had relatively good wages in the recent past participate more often in unpaid overtime. The authors also show that participati...