Police were searching late Saturday for the shooter. The incident was captured on surveillance video. A motive for the shooting wasn't immediately clear.
The victim was identified as Ronald A. Morales, of Chicago's Portage Park neighborhood, according to the Cook County Medical Examiner's Office.
The shooting occurred just before 5 p.m. at a BP gas station at the corner of 75th and Grand in the western suburb.
"I heard a volley of shots maybe 10 or more," said neighborhood resident Chris Szarejko.
Investigators said trouble began when the victim pulled into the gas station in a vehicle driven by his adult son with three children in the backseat.
Another vehicle with three men inside was already at the gas station pumping gas.
Witnesses said the victim and the man pumping gas got into an disagreement as he walked into the store to make a purchase.
Police said the victim came out of the store and began to yell at the man who had been pumping his gas as he walked toward his car.
That's when both men pulled out weapons and began shooting at each other.
The victim died on his way to the hospital.