We aim to add empirical evidence to the already studied field of wage differentials between temporary and permanent workers in Spain. Our goal is to find out which determinants of wage differentials are relevant when explaining such differences. Furthermore, the endogeneity of such feature (the type of contract) is controlled for. The same exercise is done with two data sets: the ECHP and the Structure of Earnings Survey. Results show that wage differentials between temporary and permanent workers are explained by the differences in the distribution of personal and job characteristics in both groups, but not by differences in the rewards for those characteristics. These results remain mostly unchanged during the second part of the 1990s, using information from five waves of the ECHP, and are robust to different changes in the econometric specification.