Silver
More silver has been used each year than the amount mined in each year since 1990, when the amount mined each year stopped growing and its use increased. Companies that use silver have benefited from speculators who sell promises to deliver silver that does not exist, keeping prices artificially low. This is called naked short selling. The amount owed is more than all the silver in the world. The price of silver could go very high when the stored silver runs out and investors start asking for their metal back, instead of taking more I.O.U.'s.