4 Monopoly-Like Stocks in the S&P 500 Trading at a Discount

More than half the stocks in the S&P 500 are currently in negative territory for 2026. The market recovery that followed last April's tariff shock has faded, and investors are once again navigating real volatility. Yet in my experience, these are precisely the moments worth paying attention to. When broad-based selling drags down dominant businesses alongside weaker ones, the opportunity to buy quality at a discount emerges.

After screening the S&P 500 for companies with structural monopolies or near-monopolies, I identified four that stand out right now. These are not just market leaders. They operate in spaces where competition is structurally difficult, sometimes nearly impossible, and all four are trading at year-to-date losses despite their businesses remaining fundamentally intact.

1. S&P Global (SPGI) — The Toll Booth of Global Finance

S&P Global sits at the center of the financial system in a way that makes it virtually irreplaceable.

If a corporation anywhere in the world wants to issue bonds, it needs a credit rating. And the only two firms that matter for that are S&P Global and Moody's. That is not an exaggeration. Fitch exists, but its market share is marginal. This effective duopoly has persisted for decades, and no one has come close to breaking it.

The business extends well beyond ratings. S&P Global operates four distinct segments: S&P Ratings, Platts (commodity price benchmarks used globally in oil, gas, and metals trading), Market Intelligence (financial data and analytics), and S&P Dow Jones Indices, the benchmark behind the most widely tracked indexes in the world.

What makes this business so resilient is the switching cost. Financial institutions have built their workflows, risk models, and compliance systems around S&P's data. Switching to an alternative, even if one existed, would require years of re-engineering. The result is a recurring revenue stream that barely flinches during downturns.

From what I've found, the current YTD decline has nothing to do with the health of this business. The duopoly is intact. Bond issuance continues. The toll booth keeps collecting.

2. Airbnb (ABNB) — Dominant Network Effects in Short-Term Rentals

Airbnb controls 44% of the global short-term rental market, more than double its nearest competitor.

To appreciate Airbnb's position, consider this: the next largest player, Booking.com, holds roughly 18% of the short-term rental market. That gap is not merely competitive advantage. It represents a structural lead built on network effects that are extremely difficult to replicate.

The business model is remarkably capital-efficient. Traditional hotel chains must build properties, hire staff, maintain buildings. Airbnb owns nothing. Hosts provide the inventory, guests provide the demand, and Airbnb takes a commission on every transaction. This capital-light approach translates directly into strong margins and substantial free cash flow.

The network effect here works as a flywheel. More hosts mean more options for guests. More guests mean higher occupancy and income for hosts. More hosts join. The cycle reinforces itself, making it progressively harder for any new entrant to compete. Add global brand recognition across 220 countries and over 300 million users, and the moat becomes formidable.

In my analysis, the YTD price weakness reflects broader market sentiment rather than any deterioration in Airbnb's competitive position. Travel demand continues its structural growth trajectory, and Airbnb is positioned to capture a disproportionate share of that growth.

3. Microsoft (MSFT) — The Switching Cost Fortress

Microsoft has embedded itself so deeply into enterprise workflows that replacing it would be one of the most expensive decisions a company could make.

Microsoft operates across three segments: Productivity and Business Processes (Office 365, LinkedIn, Dynamics), Intelligent Cloud (Azure), and More Personal Computing (Windows, Xbox, Surface). But the real story is about two things: Office 365 and Azure.

Think about what it would actually take for a Fortune 500 company to abandon Microsoft Office. Every document template, every macro, every workflow built on SharePoint and Teams, every Outlook calendar integration, all of it would need to be rebuilt. Employees would need retraining. Years of institutional knowledge tied to Microsoft products would be disrupted. The switching cost is not just financial. It is operational, organizational, and cultural.

Azure, while second to AWS in cloud market share, is growing faster and benefits enormously from Microsoft's existing enterprise relationships. Companies already running Office 365 and Windows find it natural to extend into Azure for their cloud infrastructure.

Then there is AI. Microsoft's substantial investment in OpenAI has positioned Copilot across its entire product suite, from Word and Excel to Azure and Windows. In my view, the short-term margin pressure from AI investment spending is a concern, but the long-term revenue potential is significant. Microsoft is building AI directly into products that hundreds of millions of people already use daily.

The current share price decline is part of the broader tech selloff. Microsoft's competitive position has not weakened.

4. TransDigm (TDG) — The Monopoly Most Investors Have Never Heard Of

TransDigm manufactures FAA-certified aerospace components for which there is literally no alternative supplier.

This is arguably the most powerful competitive moat on this entire list, and most investors have never encountered the name.

TransDigm makes components for commercial and military aircraft: actuators, ignition systems, pumps, valves, and hundreds of other specialized parts. The critical detail is FAA certification. Every component used on an aircraft must be individually certified by the Federal Aviation Administration, a process that takes years and costs millions. Once a TransDigm part is certified for a specific aircraft platform, it becomes the sole approved supplier for the life of that platform, typically 25 to 30 years.

Let that sink in.

If Boeing designs a new aircraft and the actuator from TransDigm gets certified for it, every airline flying that plane must buy replacement actuators from TransDigm. There is no approved alternative. This is not a competitive advantage. It is a legally enforced monopoly, platform by platform, part by part.

The financial results reflect this reality. TransDigm generates operating margins that would be impressive for a software company, let alone a manufacturer. In the world of industrial businesses, margins like these are virtually unheard of.

The company also grows through acquisitions, consistently buying smaller aerospace component makers to add more certified parts to its portfolio. Every acquisition adds another set of monopoly positions across additional aircraft platforms.

What This Means for Investors

The current market environment is uncomfortable. Half the S&P 500 is underwater for the year. Tariff uncertainty, interest rate questions, and geopolitical risks are all real and present. The temptation to sit on the sidelines is understandable.

But here is the framework I keep coming back to: broad-based selloffs do not discriminate between companies with fragile competitive positions and those with structural monopolies. When a stock like S&P Global or TransDigm drops because the market drops, you are getting a chance to buy a toll-booth business at a discount driven by sentiment, not fundamentals.

S&P Global, Airbnb, Microsoft, and TransDigm span different industries, but they share a common thread: each operates in a market where meaningful competition is structurally suppressed. Credit rating duopolies, network-effect platforms, enterprise switching costs, FAA-certified sole-source contracts. These are moats that do not erode in a downturn.

That does not mean these stocks cannot fall further. They can. Macro risks remain. But for investors with a multi-year horizon, the combination of monopoly-like market positions and prices near 12-month lows is worth serious consideration.

The question is not whether volatility will continue. It probably will. The question is whether these businesses will still dominate their markets in five or ten years. In my analysis, the answer is almost certainly yes.