According to police dispatch reports, the armed robbery occurred at the 7-Eleven at 1404 West Pratt Boulevard, near Pratt and Glenwood.
A black male in his 40s entered store, displayed a knife with an 8-inch blade, stole $50 from the register and two packs of Newport cigarettes, said police.
Citing various sources, the crook was wearing a tan or gray-colored sweatshirt.
Authorities said the bandit was last seen headed toward the Morse “L” station.
The clerk on duty Tuesday evening, around 7:30 p.m., said he wasn't aware of the robbery.