Monday's derailment worries environmental activists, especially since it occurred in a densely-populated city.
Iris Marie Bloom, director of Protecting Our Waters, doesn't think the area could be evacuated in an emergency.
The Philadelphia derailment occurred near the University of Pennsylvania, a highway and three hospitals.
CSX spokesman Gary Sease says the industry is also concerned after several derailments involving oil from the Bakken Shale in North Dakota.
He says CSX and industry leaders recently met with U.S. Transportation Secretary Anthony Foxx about the problem.
In the meanwhile, CSX hopes to offload oil from the Philadelphia site in the next few days, weather permitting.