The Waunakee Police Department said on Saturday at about 9:40 p.m. the Shell Station at 206 South Century Ave. in Waunakee was robbed.
Police said a man entered the store with a bandana covering his face and holding a knife. He held the knife to the employee and took cash and cigarettes before fleeing.
A surveillance system still was provided by police showing the man, police said.
Police described the robber as a darker skinned man in his late teens to 20s and approximately 5 feet 5 inches to 5 feet 10 inches tall.
He wore light-colored blue jeans, a blue-hooded sweatshirt with the words "American Eagle" printed across the front with an image of an eagle between the words. He also wore black gloves with white and gray stripes extending over the knuckles and carried a dark-colored backpack.
Police asked anyone with information to call the department at 608-849-4523 or the Waunakee tips line, 608-849-2847. Callers can remain anonymous and are eligible for a cash reward of up to $500 if it leads to an arrest.