Experimental data from multiple studies show the coarsening of co-continuous, high interfacial tension fluid systems is driven by capillary instabilities. Coarsening of low interfacial tension systems follows viscosity ratio dependence consistent with the pinch-off of suspended short filaments although there is uncertainty of this interpretation. The attenuation of coarsening rates for both types follows a common dependence on phase volume fraction and viscosity ratio. Dimensional analysis provides an interpretation of the transition from linear coarsening to slower nonlinear coarsening as a balance of interfacial tension driven flow and a critical level of interconnectivity. The slowdown of coarsening is consistent with the formation of discrete domains which subsequently coexist with the remaining co-continuous structure. (c) 2016 American Institute of Chemical Engineers AIChE J, 62: 4140-4156, 2016