It is well established that the regular lamellar eutectic structure exhibits a limited range of spacings rather than a unique spacing during steady-state growth at constant velocity. The min-imum observed spacing corresponds to the extreme spacing predicted by the Jackson-Hunt (JH) theory. However, the maximum observed spacing is much less than the maximum spacing pre-dicted by this theory. In this article, the assumption of a planar interface made by Jackson and Hunt is relaxed, and the boundary element method is used to calculate the solute distribution for a curved interface. An iterative method is used to calculate the maximum spacing for which a self-consistent interface shape exists for several velocities. This maximum self-consistent spac-ing introduces an upper bound into the JH model and shows good agreement with the maximum observed spacing in the Pb-Sn system. The deepest point on the self-consistent interface shape at the maximum spacing does not lie in a deep pocket. It is below the conjunction point but close to it.