It is ironic that during the lifetime of Sir Ernest Oppenheimer, De Beers never discovered a diamond mine itself. Oppenheimers saw little point to investing profits in exploring for diamonds, since De Beers essentially made its profits from scarcity not from an abundance of diamonds. De Beers artificially restrict the flow of diamonds, both by stockpiling diamonds in their vault in London and by manipulating the open market so as to drive up the price and maintain and even increase demand by aggressive advertising campaigns for the illusion of diamonds.
Throughout its history, the company has been committed to keeping diamond prices as stratospheric levels. More than anything, it feared that if prices began to fall, diamond owners around the world would start unloading tons of gems and the market would not be able t bear the price fall and would collapse. So De Beers made sure that gems remained secure. It could do this because of the tremendous leverage it had over the world's diamond miners, who had a very few other outlets. As Ernest Oppenheimer established it, one of the cardinal principles behind the diamond inventories was that the demand for diamonds was fixed each year and waived only with the number of engagements (Read - Can De Beers its Hammerlock? by Richard A. Mechler and Deborah Stead, Business Week, September 21, 1992). Any sudden increases in the production of diamonds would therefore be added to De Beers stockpile rather than its profit.