This paper applies a game theory approach to examine the effects of a market structure change in options trading from a monopoly to a Cournot-type oligopoly that occurred in two successive periods on the Montreal exchange. We analyze the intra-day behaviour of option bid-ask spreads and find that cross-listing has a differential impact on spreads, affecting quoted but not effective spreads under oligopoly. We also find that the impact of the change in structure on effective spreads comes mostly from an increase in limit orders and is consistent with a switch from Cournot to Bertrand-type strategic behaviour for such orders. We conclude that market structure effects within an options exchange are enough to realize most of the benefits of inter-market competition even in the context of market thinness.

ABSTRACT American options on the S&P 500 index futures that violate the stochastic dominance bounds of Constantinides and Perrakis (2009) from 1983 to 2006 are identified as potentially profitable trades. Call bid prices more frequently violate their upper bound than put bid prices do, while violations of the lower bounds by ask prices are infrequent. In out‐of‐sample tests of stochastic dominance, the writing of options that violate the upper bound increases the expected utility of any risk‐averse investor holding the market and cash, net of transaction costs and bid‐ask spreads. The results are economically significant and robust.