In context, that statement doesn't mean what you think it means.
The context is an argument against regulation of some derivative markets, because of an inability on the part of speculators to corner those markets:
The Commodity Exchange Act of 1936 and its predecessor the Grain Futures Act of 1922 were a response to the perceived problems of manipulation of grain markets that were particularly evident in the latter part of the nineteenth and early part of the twentieth centuries. For example, endeavors to corner markets in wheat, while rarely successful, often led to temporary, but sharp, increases in prices that engendered very large losses to those short sellers of futures contracts who had no alternative but to buy and deliver grain under their contractual obligations. Because quantities of grain following a harvest are generally known and limited, it is possible, at least in principle, to corner a market.
It is not possible to corner a market for financial futures where the underlying asset or its equivalent is in essentially unlimited supply. Financial derivative contracts are fundamentally different from agricultural futures owing to the nature of the underlying asset from which the derivative contract is "derived." Supplies of foreign exchange, government securities, and certain other financial instruments are being continuously replenished, and large inventories held throughout the world are immediately available to be offered in markets if traders endeavor to create an artificial shortage. Thus, unlike commodities whose supply is limited to a particular growing season and finite carryover, the markets for financial instruments and their derivatives are deep and, as a consequence, are extremely difficult to manipulate. The type of regulation that is applied to crop futures appears wholly out of place and inappropriate for financial futures, whether traded on organized exchanges or over-the-counter, and accordingly, the Federal Reserve Board sees no need for it.
...
The vast majority of privately negotiated OTC contracts are settled in cash rather than through delivery. Cash settlement typically is based on a rate or price in a highly liquid market with a very large or virtually unlimited deliverable supply, for example, LIBOR or the spot dollar-yen exchange rate. To be sure, there are a limited number of OTC derivative contracts that apply to nonfinancial underlying assets. There is a significant business in oil-based derivatives, for example. But unlike farm crops, especially near the end of a crop season, private counterparties in oil contracts have virtually no ability to restrict the worldwide supply of this commodity. (Even OPEC has been less than successful over the years.) Nor can private counterparties restrict supplies of gold, another commodity whose derivatives are often traded over-the-counter, where central banks stand ready to lease gold in increasing quantities should the price rise.
In short, all he's saying is that it's very hard to restrict the supply of gold because central banks have plenty of it, and can lend it out if the demand is there, which it presumably would be if there were sudden problems getting gold for delivery on settlement of a contract. Therefore, it would be unnecessary to regulate gold derivatives.
Testimony:
http://www.federalreserve.gov/boarddocs/testimony/1998/19980724.htm
