AbstractPorous media have properties with heterogeneities on several length scales. It is possible to build digital models of such properties. However these can be so detailed that a computing machine of the same power as that used to build the property model is not able to solve the fluid flow equations using standard discretisation methods—storage is needed for workspace, and the discrete equations have to be solved in a reasonable time. This paper reviews averaging techniques, devised to simulate large scale features of solutions without necessarily solving all the fine scale equations. Copyright © 2002 John Wiley & Sons, Ltd.