Authorities don't know why the BMW crossed into incoming traffic and collided with the tanker truck, triggering a fuel spill.
Two people were injured, one seriously, in a head-on collision Tuesday that triggered a fuel spill near Hemet.
The wreck occurred about 2:40 p.m. on Highway 79, near Stetson Avenue, in the unincorporated community of Green Acres, authorities said.
A BMW going south on Highway 79 inexplicably crossed into oncoming traffic, slamming into a northbound tanker truck, according to the California Highway Patrol.
The impact ruptured a saddle tank on the semi, spilling 60 gallons onto the roadway, the CHP said.
The motorist at the wheel of the BMW was extricated from the vehicle and taken to a hospital with broken bones, according to the Riverside County Fire Department. The trucker was also transported, for treatment of minor injuries.
Officers briefly shut down Highway 79 while crews mopped up the fuel.
The crash remained under investigation.