Speculative trading, including speculative trading in derivatives, is often claimed to provide social benefits by decreasing risk and improving the accuracy of market prices. This assumption overlooks the possibility that speculation can be driven not just by differences in traders\u27 risk aversion and information investments, but also by differences in traders\u27 subjective expectations. Disagreement-based speculation erodes traders\u27 returns, increases traders\u27 risks, and can distort market prices. There is reason to believe that by 2008, the market for OTC derivatives may have been dominated by disagreement-based speculation that contributed to the Fall 2008 credit crisis
