The model for the faulting of rocks in a three-dimensional strain field is derived here. It is assumed that the strain applied on a rock is accommodated by slip along faults. It is shown that four sets of faults in orthorhombic symmetry are required to accommodate general, three-dimensional deformation. It is further assumed that the preferred faults, namely, those which are most likely to slip, require the minimum stress difference and minimum dissipation. The orientations of these theoretically preferred faults are derived, and are compared with the experimental results of Part I (Reches and Dieterich, 1983). Good agreement is found between the predicted and observed orientations of faults in the Berea sandstone and Candoro limestone, whereas, faults in granites deviate from the predicted orientations. Good agreement is also found between predicted and observed stresses of all experiments. Charts of the preferred faults predicted by the present model are given in an Appendix.