Polystyrene-block-polyisoprene and polystyrene-block-polybutadiene form micelles in supercritical and subcritical propane that exhibit not only a critical micelle temperature (CMT) but also a critical micelle pressure (CMP). At constant polymer concentration, both CMT and CMP fall around a decreasing boundary curve in pressure-temperature coordinates. This CMT/CMP curve lies above the copolymer cloud-point curve, and below the polystyrene cloud-point curve. At the onset of micellization, a minor polystyrene impurity can cause a characteristic scattering peak as it precipitates, not only upon cooling-heating, but also upon compression-decompression. In this work experimental result of cloud point, CMT, and CMP for polystyrene-block-polyisoprene and polystyrene-block-polybutadiene is presented and compared. This work is funded by NSF Grant CTS-0244388.