The present invention is directed to completion fluid compositions and methods of making same. Such completion fluids are unique in that they utilize nanoparticles as weighting (densification) agents that increase the specific gravity (or density) of the fluid into which they are dispersed. Depending on their properties, such nanoparticulate weighting agents can vastly broaden the types of base fluid used in the completion fluid, permitting the use of non-aqueous and even hydrocarbon base fluids. Additionally, such nanoparticle-densified completion fluids can provide reduced environmental risks, and the nanoparticle weighting agents used therein can be more easily recovered from the based fluids into which they are dispersed.