In Ni, Pearson and Poteshmans' (2005) Journal of Financial Economics-article, they claim that the expiration-day price-distribution of optionable stocks is subject to inefficiencies caused by stock price manipulation and portfolio rebalancing by delta hedgers. In this thesis, two main shortcomings of Ni et al.'s (2005) study are identified. In particular, they appear to have been ignorant of fundamental microstructure factors, and they did not derive an expression to represent the theoretical price-distribution of the relevant assets. After accounting for essential microstructure variables, and calculating the theoretical distribution, results that contradict Ni et al. (2005) are found. In particular, optionable stocks are found to experience efficiency gains on expiration days, and the distribution of underlying asset prices is closer to its theoretical benchmark on expiration days relative to non-expiration days.