The probabilities of peak occurrence and binary information contents were calculated for the 43990 mass spectra in the 1987 NBS/EPA/MSDC database. The median molecular weight of compounds in the database was 230. Compounds composed of combinations of C, H, N, and O comprised 64% of the spectra. The number of base peaks per mass channel was also tabulated. A 30480 spectra subset of compounds with low molecular weights was selected as a volatile compound database. The median molecular weight of the group was 189. The probabilities and information contents of the set of spectra and the volatile hydrocarbons, oxygenated hydrocarbons, chloro compounds, and bromohydrocarbons were calculated. The most common peak in the entire database and in the volatile set occurred at mass 41. All peaks in both of these sets of spectra with probabilities greater than 0.50 occurred below mass 78. The probabilities over the total and volatile database showed a general decrease with increasing mass channel with a division into odd and even mass curves which converged at high masses. Mass channels with 0.90 to 1.0 bit information content occurred below ca. mass 100. Information contents decreased with increasing mass and the two odd and even mass curves were superimposed on the general trend.