Royal Dutch/Shell Group is under increasing pressure from investors.
They want it to unify its board as it keeps all options open concerning the overhaul its controversial dual corporate structure.
Sir John Kerr, a non-executive director, now carries out the review, and the results of this work will be known in November.
"This process requires us to look very deep and very wide at all options. We have not ruled anything out," said a Shell spokeswoman.
The group's complex dual structure -- comprised of Royal Dutch Petroleum in the Netherlands and Shell Transport & Trading in London -- has been partly blamed for the oil and gas reserves downgrade that stunned the market early this year and led to the sacking of key executives led by chairman Sir Philip Watts.
