Pentaborane, also called pentaborane(9) to distinguish it from pentaborane(11) (B₅H₁₁), is an inorganic compound with the formula B₅H₉. It is one of the most common boron hydride clusters, although it is a highly reactive compound. Because of its high reactivity toward oxygen, it was once evaluated as rocket or jet fuel. Like many of the smaller boron hydrides, pentaborane is colourless, diamagnetic, and volatile.

Pentaborane, also called pentaborane(9) to distinguish it from pentaborane(11) (B₅H₁₁), is an inorganic compound with the formula B₅H₉. It is one of the most common boron hydride clusters, although it is a highly reactive compound. Because of its high reactivity toward oxygen, it was once evaluated as rocket or jet fuel. Like many of the smaller boron hydrides, pentaborane is colourless, diamagnetic, and volatile.