Average delta hedged returns for Standard & Poor's 500 index options are large: −0.7% per day. When we decompose these option returns into intraday and overnight components, average close-to-open returns are −1% per day and open-to-close returns are positive, 0.3%. A similar return pattern holds for all maturity and moneyness categories and equity options. These positive intraday returns are particularly difficult to explain. However, our results are consistent with option prices’ failing to account for the well-known fact that stock volatility is substantially higher intraday than overnight. These findings help explain price formation in the options market.

We use tick-by-tick quote data for 39 liquid US stocks and options on them, and we focus on events when the two markets disagree about the stock price in the sense that the option-implied stock price obtained from the put-call parity relation is inconsistent with the actual stock price. Option market quotes adjust to eliminate the disagreement, while the stock market quotes behave normally, as if there were no disagreement. The disagreement events are typically precipitated by stock price movements and display signed option volume in the direction that tends to eliminate the disagreements. These results show that option price quotes do not contain economically significant information about future stock prices beyond what is already reflected in current stock prices, i.e., no economically significant price discovery occurs in the option market. We also find no option market price discovery using a much larger sample of disagreement events based on a weaker definition of a disagreement, which verifies that the findings for the primary sample are not due to unusual or unrepresentative market behavior during the put-call parity violations.