Local density augmentation around exciplex between acetophenone and N,N,N',N'-tetramethylbenzidine (TMB) in supercritical water was measured by peak shift of transient absorption spectrum at 380 degreesC and at pressures from 6 to 37 MPa. Large local density augmentation was observed at lower densities. The excess density, defined by the difference between local density and bulk density, exhibited a maximum at approximately 0.15 g cm(-1). Our results show that the degree of local density augmentation that exists in supercritical water is comparable to that observed in supercritical carbon dioxide in some system. (C) 2004 Elsevier B.V. All rights reserved.