Synthesis of copper nanoparticles within sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles was performed by implementing compressed liquid and supercritical fluid (SCF) alkanes as the bulk solvent of the microemulsion system. In this reverse micelle reaction media, the role of the anionic surfactant AOT is twofold. Initially, the AOT creates a thermodynamically stable microemulsion system consisting of water and metal ions encased within an AOT surfactant reverse micelle and dispersed within a bulk oil phase. The AOT surfactant also acts as a stabilizing ligand where the surfactant tails sterically stabilize the synthesized copper particles in solution. Our previous experimental and modeling studies have shown that the strength of the solvent interactions between the bulk liquid organic solvent and the surfactant tails affects the particle growth rate and the mean copper nanoparticle size synthesized within the microemulsion system. The thermophysical properties of compressed liquids and SCFs can be tuned through adjustments in temperature and pressure. This affords the unique ability to control particle synthesis within the reverse micelle systems by adjusting the strength of the interaction between the surfactant tails and the bulk solvent. Our results demonstrate that an increase in pressure or a decrease in temperature results in the ability to synthesize slightly larger particles. In compressed propane, the median particle diameter synthesized can be shifted from 5.4 to 9.0 nm with an increase in pressure from 241 to 345 bar. Synthesis in compressed and SCF ethane is achieved at a pressure of 517 bar and can be slightly adjusted with temperature and, even more so with the addition of a liquid alkane cosolvent. A soft-sphere modeling approach was taken to model the total interaction energy of copper particles, stabilized by AOT surfactant and dispersed within the bulk fluid, and effectively support our experimental results.