Gasker is a small uninhabited islet in the Outer Hebrides of Scotland, 8 kilometres (4+1⁄2 nautical miles) southwest of Scarp, off the west coast of Harris.

It is principally noted for its large well-established seal colony.

Residents of Scarp once visited Gasker regularly to kill seals for food.

There are two feasible landing spots for small craft: Geo Iar on the north side of Gasker, and Geodha Ear on the south side.

1.2 kilometres (5⁄8 nmi) east-southeast lies the smaller islet of Gàisgeir Beag, and some surrounding rocks.