We have determined the initial sticking probability of O2 on Pd(100) using the King and Wells method for various kinetic energies, surface temperatures, and incident angles. The data suggest two different mechanisms to sticking and dissociation. Dissociation proceeds mostly through a direct process with indirect dissociation contributing only at low kinetic energies. We suggest a dynamical precursor state to account for the indirect dissociation channel, while steering causes the high absolute reactivity. A comparison of our results to those previously obtained for Pd(111) and Pd(110) highlights how similar results for different surfaces are interpreted to suggest widely varying dynamics.