The incident occurred around 2:00 a.m. at the refinery located in the 3100 block of Passyunk Avenue.
Sunoco officials say there was a problem in a processing unit at the refinery, causing a mist of diesel fuel to be released into the air.
The processing unit was quickly shut down with no injuries or environmental concerns.
However, there was a clear oily residue found on some 150 vehicles parked in the Wilson Park area of the refinery.
Sunoco officials have gone door to door into the neighborhood to inform residents of the situation.
The refinery is operating normally except for the processing unit.