It happened around 6:15 a.m. on Kirkwood Highway at Farrand Drive in Pike Creek.
Police said the driver hit a manhole cover that was askew, causing him to roll over.
The truck was carrying oil which subsequently spilled onto the highway.
Officials said the driver of the truck required advanced life support care at the scene. He was treated for chest injuries, as well as injuries to his left extremities. He was then taken by ambulance to Christiana Care Hospital in stable condition.
Kirkwood Highway is closed in both directions at that location and officials said it will be for most of the morning.
Motorists are advised to avoid the area if possible.
Delaware State Police continue to investigate the incident.