Lanthanum strontium manganite (LSM) is widely used in cathodes of solid oxide fuel cells (SOFCs) because of its long-term stability and performance at higher operating temperatures (850-900 degrees C). The conductivity of LSM depends on the Mn valence, which in turn depends on the level of strontium doping, the ratio of (La+Sr) to Mn, and the operating environment of the cell (temperature and atmosphere). Consequently, determining Mn valences is a key issue in understanding the relationship between conductivity and operating conditions. Although the defect chemistry of LSM has been investigated extensively, this study is the first that compares new measurements of Mn valence from two direct, independent techniques: X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS). Furthermore, we have examined surfaces and interfaces of LSM in cathode-symmetric SOFCs, and XPS results from surfaces in LSM exposed to a range of atmospheres and temperatures. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3625279] All rights reserved.