Serious difficulties have been encountered in attempts to measure the absorption coefficients of sound absorbing ceilings in large offices. An analysis of the sound field is made and it is concluded (1) that the reverberation time formula is usually invalid if the absorption is concentrated on one surface of the room, (2) that the energy density formula is not subject to such a restriction and (3) that under such conditions there is no apparent field method of determining the absorption coefficient that will serve as an accurate check on laboratory measurements.