Efficient methods for the evaluation of collision, escape, and transmission probabilities in the flat-flux, isotropic approximation have been developed for various heterogeneous pin cells. The cells may be either cylindricalized or square with the moderator treated as either a single region or subdivided into the four segments between the diagonals. The conventional “Flurig” scheme by Carlvik is applied to the circular regions and to the four partial surfaces in the cylindricalized cases. For the noncircular regions and surfaces of the square-cell types, the numerical integration in both the radial and the angular direction is based on Gaussian quadrature. The mesh layout is designed with due regard to the directions to corners and vertices to avoid overlap between neighboring regions or surfaces. For rays outside the circular regions, the integration in the radial direction is performed analytically. Furthermore, the symmetry properties as well as the reciprocity and conservation relations are utilized to the maximum possible extent. Thus, high efficiency is achieved, requiring only a few mesh points in both directions as demonstrated by application to various test cases from the literature.