The accidents happened within a mile-and-a-half-stretch between the B4047 and the A415 at Witney, three days after Christmas.
Debbie Blood, 54, from Gloucester, was in a car that crashed into the back of a stationary lorry.
Four other people were taken to hospital and 15 people treated at the scene, the ambulance service said.
The driver of the lorry, Sauklius Gajauskas, had activated his hazard lights because he had seen a collision ahead.
Ms Blood's partner, Shane Giles, was driving the car and told her inquest he saw the outline of the lorry, but not the hazard lights.
PC Ross Clarkson was called to the scene and said he saw debris on the road from several collisions.
He added that visibility was only about 50m and driving conditions were "treacherous".
His statement read: "The enormity of the collision dawned on me. I could see people sat in vehicles, walking around and slumped on the ground in shock."
Oxfordshire Coroner Darren Salter said black ice and dense fog led to "awful" driving conditions.
However, he said he was satisfied the Highways Authority had acted responsibly in salting the roads on 27 December, the evening before the crash.
He concluded that Ms Blood had died as a result of a road traffic collision.
"Treacherous" road conditions caused four crashes involving 21 cars in which a woman died on the A40 in Oxfordshire.