Analyses of the composition of gaseous inclusions in ten samples of natural diamonds have been made by mass spectrometric techniques. The primary or secondary nature of the inclusions was not determined with certainty. Analyses were made by crushing the diamonds in the high vacuum inlet system of a research mass spectrometer. The gases observed were composed of C, H, O, N, and Ar atoms. Water was the most abundant gas, followed in decreasing abundance by hydrogen, carbon dioxide, methane, carbon monoxide, nitrogen, argon, ethylene, ethyl alcohol, butene, and oxygen. By generalizing from the results and assuming the inclusions to be primary, some suggestions are made which specify conditions under which natural diamonds may have been formed. A model consisting of reactions of H-C-O atoms is given as a possible explanation for the observed gas.