The purpose of this study is to find out if the stock market is efficient or inefficient with regard to product announcements. The Efficient Market Hypothesis (EMH), which states that all available information is "fully" represented in a securities price, has been a widely debated subject within the financial world and has yet to be disproved. This study includes an examination of whether or not stock prices overreact to product announcements creating abnormal returns. Two methods are applied to calculate daily abnormal stock returns and then observed over multiple days to ensure that the full announcement effect was captured. Of the 276 product announcements examined, results indicate that stock prices do overreact to product announcements, thus refuting the widely accepted EMH.