Indexes · Large cap
S&P 100, The Options-Market Hundred
A hundred of the largest members of the S&P 500, selected partly for having liquid options. Its concentration is not a flaw to be excused; it is what the index was built to provide.
Where it sits in the family
Four indices share one methodology and one committee: this hundred-name subset, the 500, the 400 mid-cap index and the 600 small-cap index, with the last three combined as the Composite 1500. The eligibility rules (domicile, listing, float, liquidity and positive earnings) are the same throughout, which is what makes them comparable with one another and not with the Russell family.
Within that family this index is the odd one out, because the other three are size bands and this one is a purpose-built subset. The 500, 400 and 600 divide the market by capitalisation and together describe it; the hundred-name index overlaps entirely with the largest of them and exists for a reason outside measurement. It is the only member of the family whose count was chosen for tradability rather than for coverage.
A subset with a purpose
The index holds around a hundred of the largest constituents of the S&P 500, chosen by the same committee. Size is the main criterion and it is not the only one: constituents are also expected to have liquid individual options, which points at what the index was for.
It was built as a reference for derivatives rather than as a portfolio benchmark. A basket of a hundred very large, heavily traded names is far cheaper to replicate and to hedge than one of five hundred, and index options on it have traded actively since the early 1980s. Concentration, which is a criticism of a benchmark, is a design requirement here.
What its existence proves about the parent
The most useful thing about this index is what it demonstrates about the one above it, and it requires no calculation to see.
If a hundred-name subset moves almost identically to a five-hundred-name index, then the parent was never delivering exposure to five hundred companies in any practical sense. The 400 smaller members contribute so little to a value-weighted number that their presence or absence barely registers. That is capitalisation weighting doing exactly what it does, made visible by a coincidence of index design.
It is also the argument for the whole breadth section in one sentence. If you want to know what most companies did, no weighted index will tell you, not the hundred-name version, not the five-hundred-name version, and not the fifteen-hundred-name version either.
Concentration limits, and why this index has none
It is worth contrasting this construction with the Nasdaq 100, which holds a similar number of companies and does something extra: it applies concentration limits, redistributing weight when the largest members exceed a set share, with a special rebalance when those limits bind.
This index has no such mechanism. It is straightforwardly float-weighted, so if the largest constituents grow relative to the rest, their share of the index grows with them without limit. Neither approach is wrong. Capping is a deliberate distortion introduced to serve funds with diversification requirements, and not capping is the more faithful measurement of what the market actually did. Knowing which one a hundred-name index uses matters more than the count itself.
Where it is actually encountered
| Use | Why this index |
|---|---|
| Index options and futures | A hundred liquid names is cheap to hedge and to replicate; the options market on it dates back to the early 1980s. |
| Volatility research | That long options history produced one of the earliest usable implied-volatility series, which older literature is built on. |
| Large-cap exposure | Defensible if the largest American companies are specifically what is wanted, and narrower than the parent for no measurable difference in behaviour. |
| Benchmarking a portfolio | Rarely the right choice. The parent or a broad-market index answers the question better. |
What a hundred names does to volume comparisons
One practical consequence for anyone reading volume rather than returns. The constituents of this index are among the most heavily traded securities in the world, which makes it the cleanest population on which the volume measures in this library behave as their descriptions assume.
Thin books, prices set by a handful of prints, and readings that describe a few trades rather than a market, the cautions that appear in every "where it misleads" table. Are largely absent here. That is worth knowing when a measure is being tested: a volume indicator evaluated only on names like these will look considerably better than the same indicator applied to a small-cap universe, and the difference is liquidity rather than the indicator.
Why it earns a page in a volume reference
Two reasons, and neither is about the index as an investment. It is the cleanest demonstration in this section of what value weighting does to exposure, a point every other index page here has to argue and this one simply shows.
And it is a reminder that indices are built for purposes. This one exists because derivatives needed an underlying that could be hedged, which is a completely different requirement from measuring a market. Reading any index number without knowing what it was built for is the same error as reading an indicator without knowing what it was built to detect.
Frequently asked questions
What is the S&P 100?
A subset of the S&P 500 holding around a hundred of its largest constituents, selected by the same committee. Companies are chosen for size and for having liquid individual options, which is the clue to what the index is for: it was built as an options and index-derivatives reference rather than as a portfolio benchmark.
Why would anyone want a hundred-name index?
Because concentration is useful when the index is the underlying for a derivative. A hundred large, heavily traded names with liquid single-stock options is far easier to hedge and to replicate than five hundred, and the tracking cost of a basket falls sharply with fewer members. What is a weakness in a benchmark — narrow exposure to a handful of very large companies — is close to a requirement here.
Is it just the top hundred of the S&P 500?
Not mechanically. It is a committee selection from the 500, weighted towards the largest names but with the options-liquidity consideration in the mix, so it is not simply the hundred largest by market value. As with its parent, membership is not reproducible from published rules alone.
How closely does it track the S&P 500?
Closely enough that the difference rarely shows on a daily chart, because both are capitalisation-weighted and the largest constituents dominate each. That is the point worth taking from it: a 500-name index and a 100-name index built from its largest members are not meaningfully more or less diversified in terms of exposure, the 400 smallest members of the parent contribute very little to its number either way.
What does that say about the parent index?
More than it says about this one. If a hundred-name subset tracks a five-hundred-name index almost exactly, then the five-hundred-name index was never providing exposure to five hundred companies in any practical sense. It is the clearest available demonstration of what capitalisation weighting does, and it is visible without computing anything.
Why does its options market matter?
Because index options on it have been actively traded since the early 1980s, and that history left a long, usable record of implied volatility, the kind of series that volatility research is built on. Anyone reading older volatility literature will meet this index for that reason rather than as a benchmark, and it is why a hundred-name index has more written about it than its size would suggest.
Should I use it as a benchmark?
Rarely, and only if the exposure you want is genuinely the largest American companies. As a measure of the American market it is narrower than its parent without behaving differently, which is the worst of both. You accept the concentration and gain nothing measurable for it. The parent, or a broad-market index, answers the benchmark question better.
Where do I get the constituent list?
From S&P Dow Jones Indices, or from the holdings of any fund tracking it. Not reproduced here, for the same reason as everywhere in this section: membership changes as events require, so a static table is wrong continuously, and a current list used on historical data drops every company that was deleted.