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S&P 100 Index (OEX) is a stock market index that tracks the performance of 100 of the largest companies in the United States. Maintained by S&P Dow Jones Indices, it includes large-cap, highly liquid corporations selected from the broader S&P 500 (SPX) universe.
The index was designed to represent some of the most influential companies in the U.S. market and became widely recognized as a benchmark for options trading and other financial products.
Because it focuses on established market leaders, the OEX is often used as a measure of the performance of U.S. blue-chip stocks.
How the S&P 100 Works
The S&P 100 is composed of approximately 100 companies selected from the constituents of the S&P 500 (SPX).
Selection emphasizes large market capitalization, strong liquidity, and active options trading activity. Like the S&P 500, the index is weighted by free-float-adjusted market capitalization.
Some of the companies commonly included in the index are:
The composition is reviewed periodically by S&P Dow Jones Indices to ensure it continues to represent some of the largest and most actively traded companies in the United States.
What the OEX Represents
The S&P 100 is used as a benchmark for tracking the performance of leading U.S. corporations.
Because its constituents include some of the most established and globally recognized companies, the index often reflects the performance of businesses with significant economic influence and international operations.
For this reason, the OEX is widely followed by institutional investors, portfolio managers, and derivatives market participants.
How to Invest in Companies Represented by the OEX
Investors cannot purchase the index directly. However, they can gain exposure to its constituents through ETFs, mutual funds, and individual stocks.
Because the S&P 100 overlaps significantly with the S&P 500 (SPX), many investors use S&P 500-based investment products to access a large portion of the companies represented in the index.
OEX Compared to Other Indexes
The S&P 100 is more concentrated than the S&P 500 (SPX) because it tracks a smaller group of large-cap companies.
Compared with the Dow Jones Industrial Average (DJI), it offers broader diversification through a larger number of constituents and sectors.
When compared with the Nasdaq-100 (NDX), the OEX generally provides a more balanced sector allocation and lower concentration in technology companies.
Why the S&P 100 Matters
The OEX remains an important benchmark within the U.S. financial markets and continues to play a significant role in options and derivatives trading. Its focus on highly liquid, large-cap companies makes it a valuable indicator of the performance of some of the most influential corporations in the world.
By bringing together industry leaders across multiple sectors, the index offers investors a useful perspective on the U.S. blue-chip market.