It has rough, flaky or fibrous bark on the trunk, smooth grey bark above, linear to narrow lance-shaped adult leaves, flower buds in groups of nine to fifteen, white flowers and urn-shaped fruit.Eucalyptus kochii is a mallee that typically grows to a height of 8 m (26 ft), rarely a tree to 12 m (39 ft), and forms a lignotuber.

[5] The specific epithet (kochii) honours Max Koch for his "very keen interest in the flora of South and Western Australia".

kochii in the Journal of the Royal Society of Western Australia, but the change has not been accepted by the Australian Plant Census.

yellowdinensis, publishing the names in the journal, Australian Systematic Botany.

[11][12] The five subspecies names recognised by the Australian Plant Census are: Oil mallee is found on flats, depressions, rises and along roadsides from Kondut to near Pindar in the Avon Wheatbelt and Yalgoo biogeographic regions of Western Australia where it grows in sandy-loamy-clay soils over laterite or granite.