The continued increase in the use of metals over the twentieth century has led to a substantial shift from geological resource base to metal stocks in society. This report reviews the relevant literature on this topic. From a compilation of 54 studies, it is clear that a reasonably detailed picture of in-use stocks and in-use lifetimes exists for only five metals: aluminum, copper, iron, lead, and zinc. Limited data suggest that per capita in-use stocks in more developed countries typically exceed those in less-developed countries by factors of five to ten.