Sussex County emergency officials say the derailment happened about 9:45 a.m. Wednesday on the tracks along Wilson Farm Road.
No leaks or injuries were reported.
One of the derailed cars, a tank car, was carrying propane. The other seven freight cars were carrying gravel.
The derailment prompted a precautionary evacuation of a number of homes, officials say.
Evacuees are reporting to the Bridgeville Volunteer Fire Company at 311 Market Street.
The Red Cross of the Delmarva Peninsula will provide assistance to evacuees, as needed, at the fire company.
Officials closed off Wilson Farm Road and Wesley Church Road to traffic.
The Sussex County Emergency Operations Center and Sussex County Emergency Medical Services are assisting Bridgeville Fire Company in the response with the County's mobile command unit and personnel.