An overturned, double tanker caused a traffic jam on the southbound on-ramp of Highway 101 at Clark Avenue in Santa Maria.
It happened about 10:15 Tuesday morning.
An official with Santa Barbara County Fire said the rear of the two tankers flipped on its side, but the cab and front tanker remained upright.
An estimated 20 gallons of crude oil spilled but did not reach any storm drains or creeks. However, the county's Hazardous Materials Unit was notified while firefighters contained the spill.
A vacuum truck was called in to offload the remaining oil.
Crews tried to get the tanker trailer back on its wheels, but couldn't. They had to call in a specialized piece of equipment from Bakersfield to upright the trailer.
The driver of the truck was not injured but a hitchhiker standing on the on-ramp was struck by the trailer and suffered minor injuries.
The unidentified man was taken to Santa Maria Marian Medical Center via American Medical Response Ambulance.
The cause of the accident is being investigated by the California Highway Patrol.