The photon‐photon optical depth for gamma‐ray bursts at cosmological distances is potentially so large that accurate calculations are needed to evaluate the conditions for which high energy photons can escape. one must explicitly included the rest frame emission pattern and determine the photon field at each point along the path of a high‐energy ‘‘test’’ photon to the observer. Relativistic expanding shell models have a key advantage over static relativistic wind models. For an expanding shell there is a sudden decrease of the optical depth with increasing Lorentz factor when the surface that contributes photons to the path of the test photon no longer subtends more than a critical angle regardless of how close the test photon is to the shell. As a result, expanding shell models require smaller relativistic flow rates than stationary surfaces. The minimum Lorentz factor that models must provide is roughly 100 for a 100 MeV photon to escape. We have made two crucial assumptions which require further study. The spectrum has been assumed to be a power law and a two component power law or a power law with a high‐energy cut‐off would decrease the required &ggr;. The expanding shell model uses a infinitly thin emitting surface and one with a finite thickness would increase the required &ggr;.