The major difference between the two stamps is the solvent that is used to mix the ink color. The self-inking stamps use water-based ink while the pre-inked stamps use oil-based ink. The action of the self-inking stamps takes place by transferring the ink from a pad inside. For the pre-inked stamps, the impression pad and the ink cell are both built into one. So when you use the stamps next time on your computer checks, you know exactly how they function.