Abstract: An improved process for the production of carboxylic acids and dicarboxylic acids by the catalytic oxidation of olefins and vicinal diols by hydrogen peroxide is provided. The process employs a rhenium (VII) catalyst, and a solvent comprising a mixture of a carboxylic acid or anhydride having 2 or more carbon atoms and a high boiling cyclic or acyclic ether. Particularly suitable carboxylic acids or anhydrides include acetic acid, propionic acid and acetic anhydride. Particularly suitable high-boiling ethers include 1,4-dioxane and diglyme.