High dropout rates, delay, and dissatisfaction among PhD students are common problems in doctoral education. Research shows that many different factors are associated with doctoral success, but these factors have not often been studied simultaneously. Moreover, characteristics of the PhD project are mostly neglected. In this study, we investigate which supervision, psychosocial, and project characteristics are related to satisfaction, progress, and quit intentions in a sample of 839 PhD candidates at a university in the Netherlands. Results of regression analyses show that experienced workload was negatively related to satisfaction and progress and positively to quit intentions. The quality of the supervisor-PhD candidate relationship, the PhD candidate's sense of belonging, the amount of freedom in the project, and working on a project closely related to the supervisor's research were positively related to satisfaction and negatively to quit intentions. The high workload of PhD candidates should be a major point of attention for universities who wish to increase their rates of PhD completion and PhD candidates' satisfaction. In addition, the 'match' between PhD candidate and supervisor is crucial, both personally -- a good relationship -- and academically, i.e. that the PhD candidate works on a topic closely related to the supervisor's research.