We report experimental cloud-point and spinodal data on the solubility of (polystyrene + nitroethane) as a function of temperature (265 < T/K < 345), weight fraction of polystyrene (0 < w(ps) < 0.30), pressure (0 < p/MPa < 6.5), polystyrene (PS) molecular weight (13 000 < M-w/a.m.u. < 130 000), and H/D isotope substitution on PS and/or nitroethane. A new high-precision apparatus based on a LASER light scattering technique was built and is described. Only phase transitions of the UCS type have been experimentally observed. Apparently, nitroethane degrades at high temperatures (T approximate to 420 K). Results show that the effects of increasing pressure or increasing the degree of deuteration on the polymer increase miscibility. In contrast, solvent deuteration decreases miscibility. Nitroethane stems to be a theta-solvent for polystyrene and therefore does not present any hypercritical temperature within the range of conditions of the experimental measurements, which have included the study of solutions slightly under tension.