An existing ASTM method for determining total oxygen in coal, indirectly from an ash analysis, was found not completely applicable for solid wastes samples, especially if the normal procedure of ashing solid wastes samples at 600 C is involved. With modifications of the formula in the ASTM method, total oxygen can be reasonably estimated in solid wastes samples. However, before a formula can be applied, the concentrations of total carbon, hydrogen, nitrogen, sulfur, and chlorine must be determined. Likewise, the analyst must have knowledge of the ash value for the sample and the procedure by which it was ascertained. Two modifications of the ASTM formula were required for solid wastes samples. The method used to determine the ash value dictates the appropriate formula because partial decomposition of carbonates occurs at 600 C. The results obtained with these formulas are affected by the errors incurred in the data obtained by the various analyses. However, this indirect approach is satisfactory and practical with solid waste samples.