Gamma ray spectra measured by the Mars Odyssey gamma ray spectrometer while in orbit around Mars were analyzed to identify the sources of 334 observed peaks and features. Most peaks were of a standard Gaussian shape with a low-energy tail. However, Doppler-broadened and sawtooth-shaped peaks were also observed in the spectra. The sources of most peaks were identified. Many peaks come from the gamma ray detector material or materials around the detector, particularly Ti and Mg. Identifications were often confirmed by analyzing other spectra, such as those measured during the cruise to Mars, before and after the boom deployment, at the end of solar particle events, and over thick frozen CO2 polar caps during winters.