Polystyrene, polybutadiene, polyisoprene, and their diblock copolymers can form compressible homogeneous solutions in propane that separate upon decompression into a solvent-rich phase and a polymer-rich phase. If the styrene block is large enough, the diblock copolymers can also form a pressure-tunable micellar nanophase that exists be-low the micellization pressure but above the cloud-point pressure. The onset of micelliza-tion and cloud-point transitions can be realistically estimated within a Statistical Associ-ating Fluid Theory (SAFT1) framework using universal SAFT1 parameters characteristic of the segment volumes and segment energies, except for the segment-segment interac-tion energy between the two blocks, which requires an adjustment to account for different types of cloud-point and micellar transitions.