Electron attachment to NO was studied in supercritical ethane at 33, 37, and 47 degrees C as a function of pressure (35-110 bar). The rate constant for electron attachment increases with increasing pressure at all temperatures studied. The most dramatic increases are observed near the critical pressure. The activation volume for this reaction is negative and quite large in magnitude, especially in this region. The activation volume depends on the isothermal compressibility. The results are compared to volume changes predicted by a compressible continuum model.