Oxygen was determined in six coals from the Wyodak Bed, Campbell County, Wyoming. Data from the U.S. Bureau of Mines' coal analysis reports were used to calculate the material balance of these coals based on accurate oxygen determination by a fast-neutron activation method developed at the University of California, Irvine. A computer program recalculates the data based on moisture determined in our laboratory and tabulates the results, comparing the 'oxygen by difference' to oxygen determined on 'as received' basis. Oxygen in samples dried at 105°C was also determined in order to estimate the possible effect of oxidation and loss of volatile components other than water during the drying process. Summations of all data were derived using the accurate oxygen values determined. This approach permits a better interpretation of stoichiometry of coal analysis. The completeness of an analysis can be thus evaluated rapidly. One may be able to indicate and pinpoint probable errors in the determination of sulphur and nitrogen in coal, also the presence of considerable CaC03. The gross effect of evolution of CH4 and gases other than H$I can be detected. One also is able to estimate the composition of the coal ash and the low-temperature ash as well as the mineral matter (Parr basis) in terms of their varying total oxygen and cation contents. This work shows that five of these six soft, water-rich, coals (20-31% H20, 105°C) do balance well stoichiometrically. One coal does not balance based on USBM moisture data. This is apparently due to an error in the moisture determination because oxygen data on this 'as received' versus 'dried, 105°C' coal match very closely. It is shown how adding the oxygen determination to routine coal analysis may permit the coal chemist to interpret the data better in terms of true material balance. Oxygen is the only major constituent not routinely determined during the ultimate coal analysis. Adding this element permits the chemist to ascertain the accuracy of the analysis, completes the analysis in the sense of stoichiometry, and makes the customary summations of coal analysis more meaningful.