Applications of shell structures to many engineering fields have introduced the problem of analyzing thick elastic shells. A useful tool for describing shells is tensor analysis. By using such a tool, a formulation based on power series expansions for displacements is developed. The resulting equations may be considered as a recurrence group, permitting the obtaining of the series coefficients in terms of six principal variables. These principal variables are the three middle surface displacements, and the three rotations about the base vectors. The equations for the thick shell theory are developed for the geometrical nonlinear case. The engineering solution of such equations can be obtained by using a cartesian reference frame.