The rollerball pen was initially designed to combine the convenience of a ballpoint pen with the smooth "wet ink" effect of a fountain pen. These writing instruments which use ball point writing mechanisms with water-based liquid or gelled ink, as opposed to the oil-based viscous inks found in ballpoint pen. The characteristics of these less viscous inks, which tend to saturate more deeply and more widely into paper than other types of ink, give rollerball pens their distinctive writing qualities.