According to some examples a substance displacement apparatus may comprise a gas ejection aperture and a deflector arm. The gas ejection aperture may be to direct gas towards a roller having a surface on which a substance is disposed. The deflector arm may be moveable between a first position in which gas is directed away from a target area on the surface of the roller, and a second position in which gas is directed towards the target area on the surface of the roller, thereby to displace at least some of the substance from the surface of the roller within the target area. A method and a print apparatus are also disclosed.