The collision happened between junction 7 for Great Barr and junction 6 at Spaghetti Junction on Wednesday morning and resulted in two lanes being closed.
However, National Highways announced at 12.30pm all lanes were back open but there were seven miles of tailbacks.
National Highways tweeted at 10.47am: "Two lanes closed on the #M6 southbound between J7 and J6 due to a collision involving 2 lorries. Just over 4 miles of congestion on approach to the incident."
At 12.30pm it confirmed the motorway was back open but warned motorists to expect delays.
It said: "Please allow time for delays to ease, approx. Seven miles of congestion remains. Allow an extra 30 minutes on to your current journey time."