##  [# Bigger Is Better: OEF Doubles In Size As Mega-Caps Dominate](/sections/features/bigger-better-oef-doubles-size-mega-caps-dominate) 

 

# Bigger Is Better: OEF Doubles In Size As Mega-Caps Dominate

 

 

Investors are pouring money into OEF as megacap tech continues to dominate the market.



 

 

 

 

 [![sumit](/sites/default/files/styles/author_image_icon/public/2023-03/Sumit_0.png?itok=SO-7S5SH "sumit")](/authors/sumit-roy) 

[By Sumit Roy ](/authors/sumit-roy)

 Oct 16, 2025

 Edited by: ETF.com Staff

 

 

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A narrower slice of the stock market is having a blockbuster year, suggesting that instead of worrying about market concentration, some investors are leaning into it.  
  
The [**iShares S&amp;P 100 ETF (OEF)**](/oef) has taken in more than $10 billion of inflows year-to-date, pushing its total assets to nearly $28 billion. Between fresh money and price gains, the fund’s assets have nearly doubled in 2025.  
  
That’s quite a turnaround for a fund that spent most of its 25-year history in relative obscurity. OEF’s assets hovered below $5 billion for much of the past two decades and only crossed the $10 billion mark at the end of 2023. Now, it’s one of the year’s biggest asset-gathering success stories.

## A Narrower, More Concentrated S&amp;P

OEF charges a 0.20% expense ratio and tracks the S&amp;P 100 Index, which includes roughly the 100 largest S&amp;P 500 companies with listed options, with modest adjustments for sector balance. Like the broader S&amp;P 500, membership ultimately comes down to the discretion of the index committee.  
  
The result is a more top-heavy version of the market. Nvidia alone makes up 10.7% of the ETF, while Microsoft and Apple weigh in at 9.3% and 9.0%, respectively.  
  
For comparison, in the [**iShares Core S&amp;P 500 ETF (IVV)**](/ivv), those three giants are 7.7%, 6.7%, and 6.5%. The 10 largest companies represent 55% of OEF’s portfolio, versus 40% for IVV.  
  
That extra dose of megacap tech has been a winning formula. OEF has gained 16% year-to-date through Oct. 15, compared with 14.6% for IVV. The gap persists over longer horizons as well: 120% vs. 106% over five years, and 335% vs. 292% over 10 years.  
  
![OEFvsIVV](/sites/default/files/inline-images/oef-ivv.png)

 
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## The Big Keep Getting Bigger

Since the financial crisis, bigger has been better. OEF’s concentration has consistently rewarded investors in an era dominated by mega-cap growth.  
  
But that hasn’t always been the case. In the period from Oct. 27, 2000, through Oct. 15, 2025, IVV leads 657% to 623%, thanks to strong performance in the decade after the dot-com crash, when smaller companies outperformed.

Over the past 15 years, though, the pattern has flipped, with smaller companies lagging as tech giants have swelled to once-unimaginable size. Whether that dominance endures is anyone’s guess. Many investors have been calling for a reversal for years, but the market keeps proving them wrong.

## Behind OEF’s Surge

Some of the recent demand for OEF may stem from model-portfolio reallocations, potentially from BlackRock itself. A staggering $3.4 billion flowed into the ETF in a single day in September, hinting at institutional or model-driven activity.  
  
OEF’s growth stands in stark contrast to funds designed to dilute concentration risk, such as the [**Invesco S&amp;P 500 Equal Weight ETF (RSP)**](/rsp), which gives each company in the S&amp;P 500 an equal weighting. RSP has seen $4.5 billion in outflows this year and has gained just 9.2% year to date and 81% over five years.  
  
Even broader funds like the [**Vanguard Total Stock Market ETF (VTI)**](/vti), which include small- and mid-caps, have lagged the most concentrated benchmarks. VTI is up 14.4% this year and 98% over five years, which is great, but still shy of the returns from IVV or OEF.  
  
The “bigger is better” era may end eventually, but judging by OEF’s surge, investors aren’t betting on that happening anytime soon.



 

 

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 [ Sumit Roy Senior ETF Analyst ](/authors/sumit-roy) 

 

 

  Sumit Roy is the senior ETF analyst for etf.com and author of (Don't) Invest Like a Pro. He creates a variety of content for the platform, including…   [View Bio](/authors/sumit-roy)

 



 

 


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