In vitro fermentation of twelve dietary fibers by fecal inocula from pigs and humans were performed. The fibers included homoglucans, mannans, fructans, polyuronides, and complex heteroglycans. Gas production, short chain fatty acid production and fiber degradation products were monitored during fermentation. Human inoculum has more ability to ferment resistant starch and fibers containing uronic acids. In contrast, pig inoculum is able to ferment cellulose, which is hardly fermented by human inoculum. The sugar and linkage composition of the fibers has an important influence on fiber fermentation patterns. Fibers containing uronic acids induced the production of acetate, whereas fibers containing neutral sugars induced the production of propionate or butyrate. Fermentation of the fructans showed that molecular size could be an influential factor, and fermentation of complex heteroglycans showed that the arrangement of sugars in the molecules may also affect the fermentation patterns. This experiment also shows that monitoring of fiber degradation products is important for understanding how fibers are degraded during fermentation.