The complex chemistry of clays and an understanding of their structures provides the opportunity for manipulating their rheological properties. The application of bentonite in the oilfield is still widespread and when used smartly can be a very effective tool. Clay is economically advantageous and environmentally friendly. Clay, when applied together with a metal oxide extender produces a truly unique fluid capable of fulfilling the most demanding hole cleaning tasks. The MMO system has to be seen in action to really believe. The fluid appears like toothpaste until it sees shear over the shakers and completely collapses releasing any and all suspended materials including cuttings and metal swarf. OS MMO and OS EXTROL combine to give the most amazing carrying capacity and fluid loss of any water based mud and at a fraction of the cost of just about any conventional mud.