300 students from Vaux Robert High School in North Philadelphia were sent home early.
Executive Chief Richard Davison said the fire department, police, and the Office of Emergency Management are working to identify the problem.
This followed a similar situation at the Annunciation School on Wharton Street.
The South Philadelphia school was briefly evacuated at around 11:30 a.m.
PGW declared there was no gas reading inside the school.
The fire department is receiving several calls throughout South and North Philadelphia about the same odor.
They are working with New Jersey health officials to see if the odor is from a massive oil spill that occurred at PBF Energy's Paulsboro refinery at 800 Billingsport Road on Thursday.
Officials say based on the way the winds are headed, it is likely this is the cause.
6.3 million gallons of crude oil spilled out of a 12-million gallon tank at the Paulsboro refinery.
Both New Jersey and Pennsylvania health officials advise there are no health issues related to the odor.