Present solid oxide fuel cells (SOFCs) use complex materials to provide (i) sufficient stability and support, (ii) electronic, ionic, and mass transport, and (iii) electrocatalytic activity. However, there is a limited quantitative understanding of the effect of the SOFC's three dimensional (3D) nano/microstructure on electronic, ionic, and mass-transfer-related losses. Here, a nondestructive tomographic imaging technique at 38.5 nm spatial resolution is used along with numerical models to examine the phase and pore networks within an SOFC anode and to provide insight into the heterogeneous microstructure's contributions to the origins of transport-related losses. The microstructure produces substantial localized structure-induced losses, with approximately 50% of those losses arising from phase cross-sectional diameters of 0.2 mu m or less. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3355957] All rights reserved.