In the present study, we examined the composition of electroencephalographic (EEG) brain oscillations in 12 unmedicated major depressive outpatients and 10 healthy subjects during resting conditions (closed eyes). The exact composition of brain oscillations was assessed by the probability-classification analysis of short-term EEG spectral patterns. In contrast to previous studies of depression, the current study found that major depression affects brain activity in nearly the whole cortex and manifests itself in considerable reorganization of the composition of brain oscillations in a broad frequency range: 0.5-30 Hz. At the same time, the magnitude of the effect of depression was maximal in the posterior cortex of the brain. Interhemisphere asymmetry during major depression was also observed in the whole cortex with right hyperactivity in frontal, parietal and occipital brain areas. It is suggested that depressive brain is manifested in the superposition of distributed multiple oscillations. Our findings provide new insight on the relationship between major depressive disorder and cortical oscillatory activity.