The dependence of edge stability on plasma shape and local pressuregradients P' in the DIII-D and JT-60U tokamaks is studied. Thestronger plasma shaping in DIII-D allows the edge region of DIII-Ddischarges with type I (giant) ELMs to have access to the secondregion of stability for ideal ballooning modes and a larger edge pedestalpressure gradient P' than JT-60U type I ELM discharges. These JT-60U discharges are near the ballooning mode first regime stability limit. The DIII-D results support an ideal stability based working model of type I ELMs as low tointermediate toroidal mode number, n, MHD modes. The results from astability analysis of JT-60U type I ELM discharges indicate that thepredictions of this model are also consistent with JT-60U edgestability observations.