Risk Arbitrage Opportunities for Stock Index Options

Research about equity index options has shown that option prices systematically violate rational pricing bounds for the risk-averse representative investor. These results raise the question of whether profitable trading possibilities exist in this market. Standard portfolio optimization does not apply because of the large bid-ask spreads and low quote sizes in this market. Motivated by these complications, a system of linear inequalities is developed that completely characterizes all risk arbitrage opportunities in the presence of transaction costs and portfolio restrictions. The practical use of this system is illustrated with an application to front-month S&P500 stock index options. Small-scale portfolios seem to produce surprisingly large abnormal returns out of sample; outperformance, however, seems elusive for institutional investors because of the limited quote size, possibly reflecting data limitations.