Mergers and acquisitions can reshape entire industries in a single deal. Over the years, some of the biggest U.S. companies have joined forces in transactions worth tens or even hundreds of billions of dollars. These deals can create new corporate giants, expand a company's reach, or bring major competitors under one roof. Here are the 10 largest mergers and acquisitions in U.S. history, ranked by enterprise value—the total value of a company, including its debt and other financial obligations.
1. SpaceX / xAI (2026): ~$250 billion
In February 2026, SpaceX acquired Elon Musk's AI company xAI in an all-stock deal that valued SpaceX at $1 trillion and xAI at $250 billion, for a combined $1.25 trillion. It set a new record for the largest M&A deal ever, passing Vodafone/Mannesmann.
How the value is made up: xAI shareholders received 0.1433 SpaceX shares for each xAI share, so the price was paid in stock rather than cash. The reported figure is a valuation of xAI as a whole. One caveat matters here: Musk controlled both companies, so the $250 billion was a negotiated internal mark, not a price set by an outside bidder.
2. AOL / Time Warner (2000): ~$165 billion
Announced in January 2000 at the height of the dot-com boom, this was an all-stock combination in which AOL, the far smaller business by revenue, bought one of the world's largest media companies. It is widely remembered as one of the worst mergers ever, and the companies eventually separated again.
How the value is made up: The ~$165 billion figure is an equity value based on AOL's stock price at announcement. Because the deal was all stock, its value swung with AOL's share price.
3. Verizon / Vodafone's Verizon Wireless Stake (2013): ~$130 billion
Verizon bought out Vodafone's 45% stake in their joint venture, Verizon Wireless, giving Verizon full ownership of the country's largest wireless carrier. It was not an acquisition of a whole company.
How the value is made up: The $130 billion reflects the price for Vodafone's stake. A record $58.8 billion of the consideration was cash, with the balance largely in Verizon stock and other assets. Verizon funded the cash portion largely by borrowing, so this deal added to Verizon's own debt load rather than assuming the target's.
4. Paramount Skydance / Warner Bros. Discovery (2026): ~$110 billion
After a five-month bidding war with Netflix, Paramount agreed in February 2026 to buy Warner Bros. Discovery (WBD), and the deal has now closed after Paramount settled legal challenges from a coalition of states and the Writers Guild of America.
How the value is made up: This is the cleanest example of equity versus enterprise value. Paramount paid $31.00 per share in cash, which implies an equity value of $81 billion. WBD carried a large debt load that Paramount took on, which brings the total to $110 billion. The roughly $29 billion difference is WBD's debt. The purchase was financed with $47 billion of new equity from the Ellison family and RedBird Capital and $54 billion of committed debt from Bank of America, Citigroup, and Apollo.
5. AT&T / Time Warner (2018): ~$108 billion
Everyone wants a piece of Time Warner, it seems. AT&T's purchase of Time Warner (HBO, Warner Bros., CNN) went through in 2018 (after being proposed in 2016) only after the Justice Department lost a lawsuit to block it. AT&T later spun the media business off.
How the value is made up: The headline figure of about $85.4 billion is the equity value paid to Time Warner shareholders. Counting Time Warner's debt brings the total to about $108 billion. The gap of roughly $23 billion is the debt AT&T took on, which, added to its own borrowing for the deal, left AT&T heavily leveraged.
6. Pfizer / Warner-Lambert (2000): ~$90 billion
Pfizer wanted full control of Lipitor, the cholesterol drug it co-marketed with Warner-Lambert, and launched a hostile bid after Warner-Lambert had agreed to merge with American Home Products. Warner-Lambert eventually accepted Pfizer's offer, and American Home Products received a $1.8 billion breakup fee.
How the value is made up: The ~$90 billion figure is a stock-based equity value.
7. Bristol-Myers Squibb / Celgene (2019): ~$89 billion
The largest pharmaceutical acquisition on record at the time combined two cancer-drug leaders.
How the value is made up: The equity value was about $74 billion. Celgene shareholders received one Bristol-Myers share plus $50 in cash for each Celgene share, plus a contingent value right (CVR) worth $9 in cash if certain regulatory milestones were reached. Including Celgene's net debt, the deal valued the company at about $88.8 billion, so roughly $15 billion of the total was debt. After closing, Celgene shareholders owned about 31% of the combined company.
8. Disney / 21st Century Fox (2019): ~$85 billion
Disney won a bidding war with Comcast to buy most of Fox's entertainment assets, including the 21st Century Fox film studio, FX TV network, National Geographic, and a controlling stake in Hulu.
How the value is made up: Disney's final offer was $38 per share in cash and stock (about half each), an equity value of about $71.3 billion. Disney also agreed to assume about $13.8 billion of net debt, for a total of about $85.1 billion at announcement. This is the one deal where the figure changed materially by closing: by March 2019, Disney said it was acquiring about $19.8 billion of cash and assuming about $19.2 billion of debt, and described the total transaction value as roughly $71 billion. The ranking uses the announcement figure, for consistency with the other entries.
9. Exxon / Mobil (1999): ~$79–81 billion
Two descendants of Standard Oil, the two largest US oil companies at the time, reunited in a stock merger announced in 1998 and completed in November 1999, after regulators required the sale of more than 2,400 gas stations.
How the value is made up: Sources report between about $79 billion and $81 billion, depending on the date and method. This was a stock-for-stock deal, so the debt is not separately broken out here.
10. Charter / Time Warner Cable (2016): ~$79 billion
Charter bought Time Warner Cable (a separate company from Time Warner, the media business) after FCC approval with conditions, creating one of the country's largest cable and broadband providers.
How the value is made up: The widely cited ~$79 billion is a transaction value that includes assumed debt, not just the price paid to shareholders. Time Warner Cable's debt made up a substantial share of that total.
Pending Deals
Union Pacific / Norfolk Southern is valued at about $85 billion, with a Surface Transportation Board decision expected in 2027. If approved, it would rank around #8.
