The S&P 100 Index is a stock market index of United States stocks maintained by Standard & Poor's. Index options on the S&P 100 are traded with the ticker symbol "OEX". Because of the popularity of these options, investors often refer to the index by its ticker symbol. The S&P 100, a subset of the S&P 500, includes 101 leading U.S. stocks with exchange-listed options. Constituents of the S&P 100 are selected for sector balance and represent about 67% of the market capitalization of the S&P 500 and almost 54% of the market capitalization of the U.S. equity markets as of December 2020. The stocks in the S&P 100 tend to be the largest and most established companies in the S&P 500. Wikipedia