The synthesis of CoO core nanoparticles from cobalt acetate is explored in alcohol solvents plus limited water using O as oxidant and NHOH as the base, all in comparison to controls in water alone employing the otherwise identical synthetic procedure. Syntheses in EtOH or t-BuOH cosolvents with limited water yield phase-pure and size-controlled (3 ± 1 nm) CoO-core nanoparticles. In marked contrast, the synthesis in water alone yields mixed phases of CoO and β-Co(OH) with a very large particle-size range (14-400 nm). Importantly, acidic reductive digestion of the CoO particles followed by H NMR on the resultant solution yields no detectable EtOH in nanoparticles prepared in EtOH, nor any detectable t-BuOH in nanoparticles prepared in t-BuOH (∼5% detection limits for each alcohol), despite the dramatic effect of each alcohol cosolvent on the resultant cobalt-oxide product. Instead, in both cases HOAc is detected and quantified, indicative of OAc as a surface ligand-and not EtO or t-BuO as the surface ligand. The resultant ROH cosolvent-derived particles were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, high-resolution transmission electron microscopy, plus elemental analysis to arrive at an approximate, average molecular formula in the case of the particles prepared in EtOH, {[CoO(CHO)][(NH)(H)]·(HO)}. The key finding is that, because EtOH and t-BuOH have a substantial effect on the phase- and size-dispersion of the cobalt-oxide nanoparticle product, yet the intact alcohol does not show up in the final CoO nanoparticle product, the effect of these alcohols cannot be a surface-ligand thermodynamic effect on the net nanoparticle formation reaction. A careful search of the literature provided scattered, but consistent, literature in which anions or other additives have large effects on metal-oxide nanoparticle formation reactions, yet also do not show up in the nanoparticle products-that is, where the observed effects are again not due to binding by that anion or other additive in a surface-ligand thermodynamic effect on the overall reaction. Alternative hypotheses are provided as to the origin of ROH solvent effects on metal-oxide nanoparticles.