The Standard and Poor's 100, or simply the S&P 100, is a stock market index of United States stocks maintained by Standard & Poor's. The S&P 100 is a subset of the S&P 500 and the S&P 1500, and holds stocks that tend to be the largest and most established companies in the S&P 500. However, the S&P 100 actually includes 101 larger US company stocks due to holding two different share classes of Alphabet Inc. 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. 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. Wikipedia