IMHO another bid is just about a certainty. Shell know this is highly likely, thus their low ball increased offer which in US$ terms is less than their previous offer.
At least we now have a firm bid on the table. We couldn't expect another bid UNTIL a formal bid was lodged by Shell.
For what its worth, I'm holding out for higher offer.
Don't forget the present BOW cash position and their interesting oil assets (particularly Cusinier).