This paper presents an experimental study on the creeping discharge propagating over the pressboard surface in two vegetable oils
(palm fatty acid ester (PFAE) oil and crude rapeseed (CRS) oil) and commercial mineral oil under the quasi-square impulse voltage
with any pulse width. It has been shown that the behavior of creeping streamers has unique characteristics and polarity effects,
and the traveling mode and propagation velocity of streamers are greatly different depending on the type of oil.