Rollerball pens use ball point writing mechanisms with water-based or gelled ink. These inks tend to have lower viscosity and tend to saturate more wide and deep into paper than other types of ink. This gives rollerball pens a distinctive writing style and quality.
Liquid-ink rollerballs use an ink and ink supply system similar to a fountain pen. They are designed to combine the convenience of a ballpoint pen with the smooth "wet ink" effect of a fountain pen.
Roller ball pens generally run out of ink more quickly than ballpoints because roller balls use a greater amount of ink while writing. This is especially true of liquid-ink roller balls, due to gel ink having a low absorption rate as a result of its thickness. Neither lasts as long as a ballpoint.