Gomphidius oregonensis, commonly known as insidious gomphidius or blackening slime spike, is a species of fungus. With age, the fruiting body becomes murky and "insidious" in appearance, hence its common name. G. oregonensis can be distinguished by its spores which are the shortest in its genus, typically less than 14 μm long. Earlier in its growth, it can be difficult to distinguish from other members of its genus, such as G. glutinosus, the most common and widespread species.

G. oregonensis is found only in western North America, most commonly on the Pacific Coast. It is edible.

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