http://www.nakedcapitalism.com/2008/06/one-method-to-flush-out-oil-speculators.html In one instance, however, the speculation premium was "successfully" tested - in the silver markets in 1980 when the Hunt brothers attempted to corner the market. As silver approached $50 an ounce in January 1980, the commercial participants asked for relief from the enormous margin calls from ever-rising prices. The CFTC and the Comex (the predecessor to the Nymex) responded effectively by imposing "liquidation-only" trading -- traders were allowed only to close existing positions and not permitted to initiate new positions. This forced purely speculative positions to be closed rapidly, as they could no longer be "rolled" into future months at expiration. This caused the price of silver to drop by $12 the day after it was imposed, a decrease of over 20%! Over the course of the next three months, as contract months expired, the price dropped over 50%.