A van carrying more than 40 cylinders of compressed oxygen and two large containers of liquid oxygen crashed with two cars near Kingswood and shut part of the A41.
Firefighters used breathing apparatus to make the scene safe but two men and two women escaped uninjured from their vehicles.
The crash happened at the Kingswood Crossroads shortly after 11am on Saturday morning. A diversion was set up taking motorists through Grendon Underwood.
The three fire crews spent more than two hours at the scene before leaving at 1.30pm.