Abstract. The integral equations encountered in boundary element methods are frequently solved numerically using collocation with spline trial functions. We apply the method of local Mellin transformation that has previously been used to derive error estimates for Galerkin methods for a wide class of operators, including those occurring in boundary element methods in acoustics, electromagnetism, and elastostatics [U]- [14]. Thus, it is to be expected that also the techniques presented here will apply to a rather large class of integral equations. For example,