Both drivers were injured in the collision.
Two cars collided on the B4022, Great Tew Road, Church Enstone on Friday morning (31/5)
A red ford Transit van was travelling towards the Tews, and a silver Vauxhall Vivaro, was travelling in the opposite direction when the collision happened.
The driver of the van, a 34-year-old man, sustained two broken wrists and a chest injury.
The driver of the car, a 45-year-old man, sustained a serious head injury.
Both are still receiving treatment at the John Radcliff Hospital.
Investigating officer PC Wayne Martin of the Road Policing team based at Bicester Howes Lane police station, said: "We are appealing for witnesses to this incident, especially anyone who saw either of these vehicles being driven shortly before this incident.
"If you have dash-cam footage of the incident or from the area at the time which shows either of these vehicles please get in touch.
Please contact Thames Valley Police on 101 quoting reference 43190163366 or make a report online."