The rollerball pen is oily and insoluble in water. It is generally used in formal occasions. For example, if you want to write on a recording disk, use an oil-based pen. The handwriting will not disappear easily. If you want to remove handwriting, you have to dissolve it with alcohol.

Gel pens are generally used in schools, public offices and other places.

If it is the high school entrance examination, candidates are generally required to use a 0.5mm black gel pen.