Methane chemical ionization (MeCI) mass spectra of several explosives, including nitrate esters, nitramines, nitroaromatics, and stabilizers, are presented. The predominance of the pseudomolecular ion (M+H) + greatly facilitates identification of these temperature-sensitive compounds. Structural effects and mechanistic pathways rationalizing formation of the major ions are included. Gas chromatographic (GC) separation of selected explosive formulations are shown. GC chemical ionization mass spectra response factors for ethylene glycol dinitrate, nitroglycerin, 2,4-dinitrotoluene, and 2,4,6-trinitrotoluene show nanogram sensitivity of this technique.