"Banksia oblongifolia" can be distinguished from "B. robur", which it often co-occurs with, by its smaller leaves and bare fruiting spikes. "B. robur" has more metallic green flower spikes, and often grows in wetter areas within the same region. "B. plagiocarpa" has longer leaves with more coarsely serrated margins, and its flower spikes are blue-grey in bud, and later bear wedge-shaped follicles. In the Sydney Basin, "B. paludosa" also bears a superficial resemblance to "B. oblongifolia", but its leaves are more prominently (spoon-shaped) and tend to point up rather than down. The leaf undersides are white and lack the prominent midrib of "B. oblongifolia", the new growth is bare and lacks the rusty fur, and the aged flower parts remain on the old spikes.