What motivates individuals to embark on graduate careers in physics and chemistry and how could these motivations impact future productivity? This study examines gender differences in such motivations and their ability to predict select future success outcomes (publications and grant funding) for physical scientists. The data were obtained as part of Project Crossover, a national study of physicists and chemists. Overall, motivations for males and females were similar. Regression results indicate that individuals who chose a graduate career in the physical sciences primarily because they enjoyed thinking about science or were encouraged by significant others were more productive in terms of primary/first-author publications and generation of grant funding than those who were motivated by factors such as academic performance or desire to impact society. (Contains 2 figures and 3 tables.)