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In this study, odorous volatile compounds (OVCs) from market-ready, commercial composts supplied by 14 different producers were compared using a recently developed method involving solid-phase microextraction (SPME) of headspace volatiles followed by GC analysis. The products analyzed were derived from a cross-section of the wide array of compost feedstock ingredients used in the U.S. (e.g., biosolids, yard trimmings, animal manure, and industrial by-products). A variety of quality assessment tests were performed using test procedures specified in a national certification program offered through the U.S. Composting Council. Measurements of odorous chemicals (i.e., trimethylamine, carbon disulfide, dimethylsulfide, dimethyldisulfide, propionic acid, and butyric acid) supplemented other quality aspects in the evaluation of stability. Result showed that relatively higher concentrations of reduced sulfur-containing compounds were detected from marketable composts containing sewage sludge than from composts produced with other feedstocks. The greatest amounts of reduced sulfur-containing compounds were detected from a compost containing a mixture of industrial sludge and agricultural byproducts. Pathogen indicator microbes for most composts were within limits for Class A (U.S. EPA 40CFR Part503). Very large numbers of fecal coliforms, E. coli, and Enterococcus were present in the compost that produced the greatest concentrations of carbon disulfide and dimethylsulfide. Composts containing sewage sludge and yard wastes produced relatively higher concentrations of propionic and butyric acids than those containing other ingredients. The composition of OVCs in compost products can be objectively evaluated with the SPME method reported here. Results in combination with other compost quality factors may help compost producers improve product quality.