Officers responded around 4:40 a.m. to the Citgo in the 3600-block of South Kedzie Avenue in the city's Brighton Park neighborhood. The 26-year-old man had been shot in the shoulder and arm, police said.
He was transported in serious condition to Mount Sinai Hospital.
Investigators are trying to find out if he was shot at the Citgo station or if he drove there to get help.
No one is in custody.