11 S&P 500 Sector ETFs Compared as One Stock Nears 25%

Owning dozens of stocks does not guarantee that their influence is evenly spread. Across the 11 S&P 500 sector ETFs, the largest security ranged from less than 7% of one fund to almost 25% of another in a September 2026 snapshot. Looking at the largest position, top three, and top ten weights reveals far more about concentration than the holdings count alone.

Key Takeaways

• Largest-security weights ranged from 6.91% to 24.69%, leaving some S&P 500 sectors far more dependent on their biggest constituent than others.

• XLY held 47 securities while its top three represented 47.75%, showing how a long holdings list can coexist with heavy concentration.

• XLE placed 73.59% in its ten largest positions, the highest top-10 concentration in the snapshot even though XLY had the biggest individual holding.

• S&P applies 24% and 50% concentration tests, while market moves can push actual weights beyond their rebalance levels between scheduled reviews.

Where Are the 11 S&P 500 Sector ETFs Most Concentrated?

The first comparison pairs the largest security with the number of fund holdings. These are fund-level figures rather than permanent characteristics because both holdings and weights can change.

The wider concentration picture changes the ranking again.

XLY had the largest single-security exposure, while XLE was the most concentrated across its ten largest positions. XLI sat at the other end, with 83 holdings and only about 40% inside its top ten. State Street reported these fund holdings as of September 8, 2026.

*XLC needs a company-level caveat. Alphabet Class A accounted for 10.28% and Class C another 8.22%. Combined Alphabet exposure was about 18.50%, slightly above Meta’s 18.00% individual security weight.

Forty-Seven Holdings Can Still Leave XLY Tied to Two Stocks

Amazon represented 24.69% of XLY and Tesla another 17.72%. Together, the two companies accounted for 42.41% of a fund containing 47 securities. Home Depot raised the top-three share to 47.75%.

Forty-seven holdings sound broad. Two positions controlled more than 42 cents of every dollar of fund exposure. Holdings count measures breadth. Weight distribution determines how much influence those holdings actually carry. You can estimate that influence with a basic return-contribution calculation.

Approximate ETF contribution = holding weight × stock return

If Amazon rose 10% while every other XLY holding stayed unchanged, a 24.69% weight would contribute roughly 2.47 percentage points to the ETF. A 10% Caterpillar move at XLI’s 6.91% weight would contribute about 0.69 percentage points under the same assumption.

The stock move is identical. The portfolio impact is more than three times larger in the heavily weighted position.

XLE Shows Why the Biggest Stock Does Not Tell the Whole Story

XLY leads on single-security concentration, yet XLE has the larger top-10 concentration. Exxon Mobil represented 19.62% of XLE and Chevron another 15.00%. ConocoPhillips brought the top three to 40.90%, while the ten largest holdings accounted for 73.59% of the ETF.

A single-stock ranking would therefore miss part of the risk. Largest-holding weight shows dependence on one security, while top-three and top-10 figures reveal whether concentration extends across a small group.

Sector structure helps explain the difference. XLE contained 21 holdings, with two companies alone representing more than one-third of the portfolio. XLI held 83 securities and its two largest positions, Caterpillar and GE Aerospace, together represented about 13.3%.

Select Sector indices start from float-adjusted market capitalisation. A sector containing several companies far larger than the rest creates greater concentration pressure before the benchmark’s caps are applied.

S&P’s 24% and 50% Tests Limit Extreme Sector Weights

The Select Sector Indices are capped market-capitalisation-weighted benchmarks. At quarterly rebalancing, S&P first calculates company weights using float-adjusted market capitalisation.

If any company exceeds 24% at the reference point, the capping process applies a 23% maximum, creating a buffer. S&P also tests companies above 4.8% collectively. Their combined weight cannot exceed 50%, with 4.5% and 45% buffers used in the redistribution process when that test is breached.

The limits apply to the underlying index methodology. The ETF seeks to track the resulting benchmark weights. A capped portfolio can still be highly concentrated. A company sitting near 23% remains responsible for almost one-quarter of the index.

Market Prices Can Push a Stock Above Its Rebalance Weight

Amazon’s 24.69% XLY weight shows why the 24% test should not be read as a permanent trading-day ceiling. Select Sector weighting uses prices from a prescribed reference date to calculate index shares. S&P notes that actual weights can differ by the time the rebalance takes effect because market prices continue moving.

The same process continues afterwards. A stock reset near 23% can gain faster than the rest of its sector and climb above that level without the fund deliberately increasing its position. Regular Select Sector rebalancing occurs after the close on the third Friday of March, June, September and December, using the Wednesday before the second Friday as the weighting reference date.

S&P also performs a secondary check on the second-to-last business day of those quarter-ending months. A company above 24%, or companies above 4.8% collectively exceeding 50%, can trigger another reweighting after the final business day.

Rebalancing periodically pulls concentration back toward the methodology. Relative stock-price moves then begin changing the weights again.

XLC Shows How Share Classes Can Hide Company Concentration

XLC demonstrates why security-level and company-level concentration are not always identical.

Its holdings list showed Meta at 18.00%, Alphabet Class A at 10.28% and Alphabet Class C at 8.22%. Reading each security separately makes Meta appear larger, while Alphabet’s two classes combine to roughly 18.50%.

S&P applies maximum-weight capping at the company level, then allocates the resulting company weight across its share classes. A concentration review therefore needs to check the underlying issuer as well as individual lines in the holdings file.

Frequently Asked Questions

Can a sector ETF lose money even if most of its holdings rise?

Yes. A heavily weighted company or small group can offset gains elsewhere when its losses are large enough. ETF performance reflects each holding’s weighted contribution, not just how many constituents rise.

Does a sector ETF rebalance whenever its biggest stock becomes too large?

No. Select Sector concentration tests operate at scheduled index reviews. Market moves can therefore push a constituent above its previous rebalance weight before the next applicable capping calculation.

Can two ETFs covering the same sector have different concentration?

Yes. Benchmarks can use market-cap, equal-weight or modified weighting rules with different caps. Funds owning many of the same companies can therefore assign substantially different weights to their largest constituents.

Does adding more stocks automatically reduce ETF concentration?

No. Additional stocks may receive very small weights while the largest companies retain most of the portfolio. Concentration falls meaningfully when portfolio weight becomes more evenly distributed, rather than simply through a longer holdings list.

What happens if one company keeps outperforming the rest of its sector?

Its weight can repeatedly rise between scheduled reviews until the benchmark’s concentration rules force another reset. Persistent recapping can therefore reflect a company growing unusually large relative to its sector peers.

The Next Rebalance Reveals How Much Concentration Came From Price Moves

The useful comparison comes after each March, June, September and December rebalance. Matching the new weights against those immediately before the reset shows how much concentration came from relative stock performance and how much remains after the index rules are reapplied. The holdings count may barely change while the concentration underneath it moves materially.