"He opened the door, and he had a gas tank with him in his hands, and he started pouring the gas everywhere, and he said, 'This is a stickup,'" said store owner Haytham Elzeibaq.
It happened at Morgan Park Foods in the 1100-block of West 111th Street.
The suspect, Thomas Hughes, Jr., was allegedly wearing a ski mask during the incident.
He's charged with attempted aggravated arson and armed robbery.
Onlookers called police.
The two men and a security guard held the suspect until police arrived.