The crash occurred shortly before 7:30 a.m. right off the 101 Freeway south of Rose Avenue.
Winds in the area are very strong, but it's not clear if that caused the semi-truck to veer off the freeway and into the lot.
Several of those parked cars caught fire. Nine vehicles were destroyed and seven others were damaged including Porsches and Range Rovers.
The damage was estimated at $1.2 million.Firefighters had to spray water and foam on the flames. There was also gasoline on fire and the truck was loaded with tissue paper, making it very flammable.
The female driver of the big rig was transported to Ventura County Medical Center. Her condition remains unknown.
No other injuries were reported.
CarMax employees were on site when the incident took place but the dealership was not yet open at the time of the accident.
Fire crews from Ventura County and the city of Oxnard were on scene working to clean up the mess and debris.
CHP is handing the investigation.