Most often mineral oil is used to store, protect reactive metals from oxidation. By far the best choice is to hermetically seal the metal in pure argon or some other inert gas, since, although mineral oil tends to slow down the oxidation process, it's still soluble to oxygen and slowly but surely the metal will begin to oxidize.
While argon is a sure thing it requires special equipment, and once sealed you have to break the container to access the metal.
My question - among liquids is there a better choice than mineral oil? A liquid that will not react with the metals, and provide a better barrier to migration of oxygen?