The men were caught on camera at two stores in Bridgeview and at other stores in Michigan and Missouri, the FBI said.
Police said they were wearing Halloween-style masks or other face coverings when they held employees at bay with an assault rifle and a hammer.
The suspects robbed two stores in Bridgeview last summer and in January, the FBI said. Then in august, police said the same crew held up a store in Dearborn, Michigan. In September, they hit a store in Winchester, Missouri.
No one has been seriously hurt during the crimes, the FBI said.
A $15,000 reward has offered by the FBI for information leading to arrests and convictions of the suspects.