||Blending parametric surfaces can be a valuable tool in sculptured surface modeling. In conventional approaches, the boundaries and the cross boundary tangents of the blending surface are obtained by approximating a discrete number of points and vectors that are evaluated along the blending boundaries. A method of surface blending is presented here to improve the quality of the blending surface by computing its boundary and tangent curves symbolically rather than by approximation. Symbolic computation techniques have been shown effective in many applications. To blend surfaces in closed form, algorithms are needed to compose curves into surfaces. Two algorithms to compose a two-dimensional NURB curve into a NURB surface will be presented. Techniques to compute the blending surface in closed form using these extended symbolic operators are also presented.