The man went into the BP garage on Norton Road, Stourbridge, and pulled out a knife at approximately 5.30pm on Sunday.
He stole cans of Lynx deodorant before fleeing the scene.
A spokesman for West Midlands Police said: "We were called following a robbery in Norton Road, Norton, at around 5.45pm on Sunday (26 March).
"A worker was threatened with a knife as deodorant was stolen.
"Anyone with information can contact us via Live Chat on our website and quote log 3065 of 26 March."