Roller ball pens are pens which use ball point writing mechanisms with water-based liquid or gelled ink, as opposed to the oil-based viscous inks found in ballpoint pens. These less viscous inks, which tend to saturate more deeply and more widely into paper than other types of ink, give roller ball pens their distinctive writing qualities. The writing point is a tiny ball, usually 0.5 or 0.7 mm in diameter, that transfers the ink from the reservoir onto the paper as the pen moves.

Advantages

Rollerball pens were introduced in 1963 by the Japanese company Ohto. There are two main types of roller ball pens: liquid ink pens and gel ink pens. The 'liquid-ink' type uses an ink and ink supply system similar to a fountain pen, and they are designed to combine the convenience of a ballpoint pen with the smooth "wet ink" effect of a fountain pen.

Gel inks usually contain pigments, while liquid inks are limited to dyestuffs, as pigments will sink down in liquid ink (sedimentation). The thickness and suspending power of gels allows the use of pigments in gelled ink, which yields a greater variety of brighter colors than is possible in liquid ink. Gels also allow for the use of heavier pigments with metallic or glitter effects, or opaque pastel pigments that can be seen on dark surfaces.