Average sound absorption coefficients were determined for the interior surfaces of concert halls based on measurements in five halls in which all finishes had been completed before installation of seats. Fifteen halls were selected for detailed analysis and divided into three groups with seats that are (1) lightly upholstered, (2) medium upholstered, and (3) heavily upholstered. Assuming relative humidites of 50% for unoccupied and 70% for occupied halls, ``acoustical'' areas (added 0.5-m edge effect) for seating blocks, and the above, average interior-surface, absorption coefficients, the sound absorption coefficients for occupied and unoccupied seats were calculated from reverberation measurements. Among the three groups, it is found that there are large differences in absorption coefficients for the seats at all frequencies, but particularly at low frequencies. The values are markedly different from those previously published [L. Beranek, J. Acoust. Soc. Am. 92, 1--39 (1992)]. Where possible, photos and visual analyses of the chairs are made to compare with the data.