A process for making cerium-containing oxide nanoparticles includes providing an aqueous reaction mixture containing a source of cerous ion, a source of hydroxide ion, at least one monoether carboxylic acid wherein the molar ratio of said monoether carboxylic acid to cerous ions is greater than 0.2, and an oxidant. The cerous ion is oxidized to ceric ion, thereby forming a product dispersion of cerium-containing oxide nanoparticles CeO2-δ, wherein δ has a value of about 0.0 to about 0.5.