Water-soluble organic compounds of atmospheric aerosol were analyzed using positive electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Ambient aerosol collected at a nonurban high elevation site near Steamboat Springs, CO. Approximately, 2400 molecular formulas were assigned to the positive ions containing carbon, hydrogen, oxygen, nitrogen, and sulfur atoms in the range of m/z 100-800. The double bond equivalents (DBE) range, mean O:C, mean H:C, and oxidation state of carbon were 0 - 18, 0.25 ± 0.15, 1.39 ± 0.29, and -0.89 ± 0.23, respectively. A majority of the CHOS, CHNOS, and CHS formulas were highly unsaturated with mean DBE values of 12, 13, and 10, respectively. A majority of the CHNO and CHO formulas were more saturated with mean DBE values of 5 and 3, respectively. Several CHNO formulas were observed to be common with those of other studies including biomass burning aerosol and aged products of limonene ozonolysis.