The dimensionless extinction constant, K-e, was measured using the NIST large agglomerate optics facility (LAOF) for soot produced from JP-8 flames. Measurements were performed using light sources ranging from 632.8 to 1565 nm. These experiments represent the first measurement of dimensionless extinction constant for soot produced from JP-8 flames. The K-e values did not display significant spectral variations that were observed for pure fuels such as acetylene and ethene. The measured K-e values ranged from 9.75 to 9.95 in the wavelength range between 632.8 and 1565 nm. Measurements provide a more reliable value of K, for use in optical-based soot diagnostics for soot concentration and temperature measurement as well as for soot radiation analysis. (C) 2004 Elsevier Ltd. All rights reserved.