According to New Castle County Police, the tanker was traveling southbound on Route 1 when it exited the roadway at Lorewood Grove Road.
Police say the driver, William Statts, 39, was travelling too fast, hit a guardrail, and overturned.
Statts was trapped for two hours as crews worked to free him.
He was then transported by helicopter to Christana Hospital where he was listed in stable condition.
The DNREC says that there were about 250 gallons of gasoline that spilled out of the tanker, and the tanker was holding 8000 gallons of gasoline.
Also, some diesel fuel may have leaked, so they are treating the soil.
Both lanes of Route 1 were closed for much of the day. The left lane re-opened at 2:40 p.m., and the right lane opened later in the evening.
Statts was cited for Unreasonable Speed.
Meanwhile, Delaware State Police were on the scene of a 4-car accident near the site of the overturned truck.
That crash has left seven people injured.
It happened Sunday afternoon at the intersection of Rt 1 and Rt 72 (Wrangle Hill Road).
The injured include small children.
Four of the seven have been taken to area hospitals, including a four-year-old and a five-year-old.
Police say the accident was caused by traffic congestion from the tanker accident.
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