This article presents the stabilization of silver nanoparticle intermediates synthesized in ammonium perfluoropolyether (PFPE-NH4) reverse micelles with supercritical fluid (SCF) carbon dioxide solvent as the continuous phase. Specifically, the intermediates were formed by the reduction of silver nitrate salt (AgNO3) encapsulated within PFPE-NH4 reverse micelles. The effect of reducing agent type, reverse micelle water content, water core buffering, and bulk solvent type were all investigated as factors affecting stabilization of the silver nanoparticle intermediates. Particles were characterized by in situ UV-visible spectroscopy and transmission electron microscopy (TEM). The UV-vis spectrum of these nanosized silver particles is sensitive to particle size, and thus time-resolved spectral measurements were utilized as a means of monitoring both intermediate growth and persistence. The silver intermediates were stabilized in PFPE-NH4 reverse micelles as indicated by multiple UV-vis absorption bands that persist for periods of time measured to greater than 9 h. Intermediate stabilization is facilitated by a unique environment existing specifically as a result of PFPE-NH4 surfactant presence and its local water environment in the reverse micelle rather than any effects arising from the carbon dioxide solvent.