We present a method for the determination of orientation-dependent mobilities Gamma(eff)(p) based upon analyses of the detachment-limited coarsening/decay kinetics of equilibrium-shaped two-dimensional islands. An exact analytical expression relating the orientation-dependence of F-eff(p) to that of the anisotropic step energies ss(p) is derived. This provides relative values of Gamma(eff)(p) to within an orientation-independent scale factor that is proportional to the decay rate of the island area. Using in situ high temperature (T= 1550- 1700 K) low-energy electron microscopy measurements of two-dimensional TiN island coarsening/decay kinetics on TiN(111) terraces for which ss(p) values are known [Phys. Rev. B 67 (2003) 35409], we demonstrate the applicability of our analytic formulation for the determination of absolute Gamma(eff)(p) values. (c) 2005 Elsevier B.V. All rights reserved.