noun
permanent marker; oil-based pen
A pen that uses oil-based ink, often synonymous with permanent markers. Compare 油性マーカー and 油性マジック, which are similar but may emphasize marker form.
油性ペンで箱に名前を書いた。
I wrote my name on the box with a permanent marker.
この油性ペンは水に濡れても
This oil-based pen doesn't smudge even when wet.