Mergers and Acquisitions Examples: The largest company M&A deals list

When it comes to mergers and acquisitions, bigger doesn’t always mean better - the examples we included in our list of the biggest M&A failures is evidence of that.

In fact, all things being equal, the bigger a deal becomes, the bigger the likelihood that the buyer is overpaying for the target company. But whether you like mega deals or not, we cannot afford to ignore them. 

At DealRoom, we help companies evolve and streamline multiple large and successful M&A deals each year. In this article, we collected some of the biggest deals in history.

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Related: Recent M&A Deals and 8 Biggest M&A Deals in History (so far) and 8 Biggest Upcoming M&A Deals in 2023 (so far)

Biggest mergers and acquisitions examples list

Reading this list, it can seem that the biggest deals are doomed to failure (at least from the perspective of their shareholders). But thankfully, that just isn’t the case. Some of the biggest M&A transactions of the past 30 years have been outstanding successes.

Many of these deals have achieved what they set out to do at the outset - to reshape industries on the strength of a single deal.

With that in mind, let's take a closer look at 25 companies that recorded the largest mergers and acquisitions in history.

1. Vodafone and Mannesmann (1999) - $202.8B ($373B adjusted for inflation)

As of March 2024, the takeover of Mannesmann by Vodafone in 2000 was still one of the largest acquisitions ever made. Worth ~$203 billion at that time, Vodafone, a mobile operator based in the United Kingdom, acquired Mannesmann, a German-owned industrial conglomerate company.

This deal made Vodafone the world’s largest mobile operator and set the scene for dozens of mega deals in the mobile telecommunications space in the years that followed. This deal is still considered as the biggest acquisition in history.

2. Shenhua Group and China Guodian Corporation (2017) - $278B ($354B adjusted for inflation)

The merger between Shenhua Group and China Guodian Corporation is the biggest example of a merger of equals that happened in 2017. Shenhua Group is China’s largest coal provider, while China Guodian Corporation is one of the top five electricity producers.

This $278 billion merger created the world’s largest power utility company by installed capacity. The goal of the merger was to create a balanced energy portfolio between coal power and renewable energy. This is to align with China’s broader environmental and economic objectives.

3. AOL and Time Warner (2000) - $182B ($325B adjusted for inflation)

When we mentioned at the outset of this article that ‘big doesn’t always mean better’, the famous merger of AOL, a U.S.-based internet service provider, and Time Warner, an American cable television company, in 2000 is a case in point. 

In little over two decades, the deal has become cemented as the textbook example of how not to conduct mergers and acquisitions. It featured everything from overpaying to strong cultural differences and even, with the benefit of hindsight, two large media companies who just weren’t sure where the media landscape was headed. 

The merger's valuation came crashing down after the dot-com bubble burst just two months after the deal was signed. The deal, which is to be known as the largest merger in history, fell apart in 2009, 9 years later after it was originally signed.

4. ChemChina and Sinochem (2018) - $245B ($309B adjusted for inflation)

The ChemChina and Sinochem merger was part of the Chinese government’s bigger plan to strengthen their competitiveness in the global stage by reducing the overall number of its state-owned enterprises through merging its biggest companies to create a larger firm.

This specific merger created the world’s largest industrial chemicals company, known as Sinochem Holdings, which surpassed major global competitors like BASF in North America in terms of scale and market presence.

5. Gaz de France and Suez (2007) - $182B ($259B adjusted for inflation)

France loves its national champions - the large French companies that compete on a world stage, waving the tricolor. It was no surprise then, when Nicholas Sarkozy, President of France in 2007, stepped in to save this merger.

That’s right - a President playing the role of part-time investment banker. These days, Suez is one of the oil and gas ‘majors’, although the fact that the company’s share price hovers very close to where it was a decade and a half ago tells us everything of what investors thought of the deal.

The deal, one of the biggest mergers ever in energy, created the world’s fourth largest energy company and Europe’s second largest electricity and gas group. The merged companies created a diversified, flexible energy supply stream with a high-performance electricity production base.

6. Glaxo Wellcome and SmithKline Beecham merger (2000) - $107B  ($197B adjusted for inflation)

The merger of the UK’s two largest pharmaceutical firms in 2000 led to what is currently the 6th largest pharmaceutical firm in the world, and the only British firm in the top 10.

However, like several deals on this list, it wasn’t received particularly well by investors and at the time of writing is trading at about 25% less than the time of the merger.

This, and a range of bolt-on acquisitions in the consumer space over the past decade, may explain why the company is planning to split into two separate companies in the coming years.

7. Verizon and Vodafone (2013) - $130B ($173B adjusted for inflation)

Vodafone has been involved in so many transactions over the past 20 years that they should be getting quite efficient at the process at this stage. The $130B deal in 2013 allowed Verizon to pay for its US wireless division.

At the time, the deal was the third largest in history - two of which Vodafone had partaken in. From Verizon’s perspective, it gave the company full control over its wireless division, ending an often fraught relationship with Vodafone that lasted for over a decade, and also allowed it to build new mobile networks and contend with an increasingly competitive landscape at the time.

From Vodafone's point of view, the acquisition cut the company value roughly in half, to $100 billion. The business acquisition also moved Vodafone from the second largest phone company in the world down to fourth, behind China Mobile, AT&T, and Verizon.

8. Dow Chemical and DuPont merger (2015) - $130B ($166B adjusted for inflation)

When Dow Chemical and DuPont announced they were merging in 2015, everyone sat up and took notice; the merger of equals would create the largest chemicals company by sales in the world, as well as eliminate the competition between them, making it a picture-perfect example of horizontal merger.

Shortly after the deal was completed, in 2018, the company was already generating revenue of $86B a year - but it didn’t last long: In 2019, management announced that the merged company would spin off into three separate companies, each with a separate focus.

9. United Technologies and Raytheon (2019) - $121B ($147B adjusted for inflation)

The merger between United Technologies Corporation (UTC) and Raytheon Company created Raytheon Technologies, an aerospace and defense giant. The new legal entity is expected to be the leader in aerospace and defense industries, with a broadened portfolio and enhanced market reach.

Now that the deal went through, Raytheon can leverage United Technologies' expertise in high temperature materials for jet engines; and in directed energy weapons, United Technologies has relevant power generation and management technology.

So far, however, investors seem less convinced with the company’s share price taking a dip of around 25% straight after the deal closed.

10. AB InBev and SABMiller merger (2015) - $107B  ($138B adjusted for inflation)

If stock price is any indication of whether a deal was successful or not, then the creation of AmBev through the merger of InBev and SABMiller in 2015 certainly wasn’t.

On paper, the deal looked good - two of the world’s biggest brewers bringing a host of the world’s favorite beers into one stable.

There was just one problem - they didn’t foresee the rise of craft beers and how it would disrupt the brewing industry. Several bolt-on acquisitions of craft brewers later and the new company may finally be on track again.

11. AT&T and Time Warner (2018) - $108B ($134B adjusted for inflation)

Not only did the proposed merger of AT&T and Time Warner draw criticism from antitrust regulators when it was announced, it also brought back memories of the previous time Time Warner had been involved in a megadeal.

With the best part of two decades to learn from its mistake, and AT&T a much bigger cash generator than AOL, this deal looks like it has been better thought through than the deal that preceded it.

12. Heinz and Kraft merger (2015) - $100B  ($131B adjusted for inflation)

The merger of Heinz and Kraft - to create the Kraft Heinz Company - is yet another megadeal that has a detrimental effect on stock.

The deal has been called a “mega-mess,” with billions knocked off the stock price since the deal closed. One of the reasons has been allegations made about accounting practices at the two firms before the merger.

Another reason has been zero-based budgeting (ZBB), a strict cost cutting regime that came at a time when old brands needed to be refreshed rather than have their budgets cut back.

13. BMO Financial Group and Bank of the West (2021) - $105B ($119.5B adjusted for inflation)

On December 20, 2021, BMO Financial Group announced the acquisition of BNP Paribas SA unit Bank of the West and its subsidiaries with assets worth approximately $105B. This merger is expected to significantly expand BMO’s presence in the U.S.

Through this acquisition, BMO can expand their customer base, increase their market presence in new regions, and enhance their existing capabilities with complementary products and services offered by Bank of the West.

14. Bristol-Myers Squibb and Celgene merger (2019) - $95B  ($115B adjusted for inflation)

Despite the massive size of the transaction, this 2019 megadeal wasn’t a “merger of equals.” Instead, Celgene became a subsidiary of Bristol-Myers Squibb. The deal brings together two of the world’s largest cancer drug manufacturers, so hopefully the deal amounts to something much greater than the sum of the parts.

15. Energy Transfer Equity and Energy Transfer Partners (2018) - $90B  ($111B adjusted for inflation)

This deal is part of a strategic initiative to simplify Energy Transfer Equity’s corporate structure and streamlining their operations.​

Each ETP unit was converted into 1.28 ETE units, resulting in a major redistribution of shares but keeping the business essentially continuous under a new name. 

ETE was renamed Energy Transfer LP and began trading under the ticker symbol "ET" on the New York Stock Exchange. On the other hand, ETP was renamed Energy Transfer Operating L.P.

16. Unilever plc and Unilever N.V. (2020) - $81B  ($97B adjusted for inflation)

The M&A deal between Unilever plc and Unilever N.V. in 2020 was essentially a unification strategy. The primary goal was to create a more cohesive organization with streamlined operations and increased strategic flexibility. 

During this process, they made sure nothing will change in their operations, locations, activities or staffing levels in either The Netherlands or the United Kingdom.

17. Walt Disney and 21st Century Fox (2017) - $52.4B ($83.7B adjusted for inflation)

In December 2017, The Walt Disney Company acquired 21st Century Fox. Walt Disney’s goal was to boost their global presence and content diversity, adding to its strong franchise and streaming service portfolio. This acquisition enhanced Disney’s entertainment library and direct-to-consumer streaming offerings, bringing franchises like X-Men and Deadpool under one roof.

18. Bayer and Monsanto (2018) - $63B ($78B adjusted for inflation)

The deal between Bayer and Monsanto worth approximately $63B created one of the world's biggest agrochemical and agricultural biotechnology corporations. Bayer was known widely for its pharmaceutical division, but it also has a substantial crop science division, where they offer chemical and crop protection. 

Through the Monsanto acquisition, Bayer has strengthened their agricultural business using Monsanto’s expertise, which ultimately made them a global leader in seeds, traits, and agricultural chemicals.

After the completion of the deal in 2018, the integration has been complex due to the legacy issues inherited from the acquisition of Monsanto, such as culture, reputation, and legal and regulatory issues.

19. Microsoft and Activision Blizzard (2023) - $75.4B ($76.5B adjusted for inflation)

On January 18, 2022, Microsoft announced its intent to acquire Activision Blizzard, initially valued at $68.7B. The goal of this strategic acquisition was to significantly boost its gaming segment across various platforms including mobile, PC, console, and cloud. 

Microsoft can do this by integrating Activision Blizzard's strong portfolio of popular gaming franchises like Call of Duty, World of Warcraft, and Candy Crush. After overcoming numerous regulatory challenges, the deal was finalized on October 13, 2023. 

This acquisition, with the total cost amounting to $75.4 billion, represents one of the largest deals in the video game industry.

20. Broadcom and VMWare (2023) - $61B ($62B adjusted for inflation)

In November 2023, Broadcom acquired VMWare to strengthen its infrastructure software business by integrating VMWare’s extensive multi-cloud services capabilities. 

Due to the large scale of both companies’ operations, the deal had to go through a massive regulatory scrutiny and review. It involved multiple jurisdictions across the globe to assess its impact on competition and market dynamics within the tech industry.

21. Exxon Mobil and Pioneer Natural Resources (2023) - $59.5B ($60B adjusted for inflation)

As part of their strategy to enhance their production capabilities and market presence in the oil and gas industry, Exxon Mobil merged with Pioneer Natural Resources. 

They announced this deal in October 2023, with the goal to achieve a partnership that would combine their strengths in terms of resources and strengthen their portfolio in the global energy market. 

ExxonMobil’s Senior Vice President, Niel Chapman, reaffirms that the deal is still on track and is set to close in the second quarter of 2024.

22. S&P Global and IHS Markit (2020) - $44B ($52.8B adjusted for inflation)

S&P Global announced an all-stock merger with IHS Markit worth $44 billion in November 2020. Through this deal, S&P Global will gain access to a data provider that supplies financial information to 50,000 customers across business and governments. Both companies expected a generated annual free cash flow of exceeding $5bn by 2023.

23. Discovery, Inc. and WarnerMedia (2022) - $43B ($46B adjusted for inflation)

On April 8, 2022, Discovery Inc. and WarnerMedia finalized a merger that would enhance their global media and entertainment footprint. The goal was to combine Warnermedia’s extensive entertainment assets with Discovery's non-fiction and international entertainment.

This $43B deal formed a new entity called Warner Bros. Discovery, which now has a vast portfolio that includes networks such as CNN, HBO, and Discovery Channel, as well as streaming services like HBO Max and Discovery+.

This horizontal merger boosted the newly formed company to compete with other major players like Netflix and Disney+ by providing a richer diversity of content across genres.

24. Pfizer and Seagen (2023) - $43B ($43.7B adjusted for inflation)

Pfizer’s acquisition of Seagen for $43B in March 2023 marked one of the largest deals in the biopharmaceutical sector since 2019.

Since Seagen is a biotech company known for its expertise in developing antibody-drug conjugates (ADCs) and other innovative cancer therapies, this acquisition will strengthen Pfizer’s oncology portfolio and expand their presence in the cancer treatment market.

25. Altimeter and Grab Holdings (2021) - $40B ($46.7B adjusted for inflation)

Altimeter’s stock-for-stock merger with Grab Holdings marked as the largest de-SPAC transaction at that time, worth approximately $40B. 

Instead of a traditional IPO process, Altimeter helped Grab go public through a reverse merger. The primary motive of the deal was to boost Grab's dominance in Southeast Asia by providing them with additional capital to propel their expansion and face their fierce competition, particularly Gojek.

It's a win-win move for Altimeter because the merger carved an opportunity for them to invest in a fast-growing tech company with a solid market presence in a rapidly developing region.

Exxon Mobil and Pioneer Natural Resources (2023) - $59.5B ($60B adjusted for inflation)

This is a great example of a merger of equals where no payment was made from one company to another. This was an all-stock transaction, where Pioneer shareholders will receive 2.3234 shares of ExxonMobil for each Pioneer share at closing.

United Technologies and Raytheon (2019) - $121B ($147B adjusted for inflation)

Another classic example of a so-called “merger of equals.” The United Technologies and Raytheon merger is also an all-stock transaction, where Raytheon shareholders receive shares in the new company, while UTC shareholders maintain a majority stake.

Discovery, Inc. and WarnerMedia (2022) - $43B ($46B adjusted for inflation)

Despite the first two examples mentioned above, not all mergers involve two equal-sized companies. When AT&T owned WarnerMedia, they merged it with a smaller company, Discovery Inc. This special kind of deal is called a Reverse Morris Trust. So even though it's a merger, AT&T got $40.4 billion in cash as a payment. 

This payment was part of the deal to help balance things out between what AT&T was giving up and what they were getting in return. AT&T shareholders also ended up owning a big part of the combined company.

Microsoft and Activision Blizzard (2022) - $75.4B ($76.5B adjusted for inflation)

This is an example of an outright acquisition. In December 2021, Blizzard faced allegations and a lawsuit regarding workplace misconduct, specifically discrimination against women employees. Their reputation and business operations were taking a hit, and they wanted an out. 

Meanwhile Microsoft wanted Activision's iconic franchises like “Call of Duty” and “World of Warcraft” to increase their presence in the gaming industry. Activision saw Microsoft’s acquisition as a way to address internal issues under new leadership, while Microsoft potentially expanding its footprint in the gaming industry.

Walt Disney and 21st Century Fox (2017) - $52.4B ($83.7B adjusted for inflation)

Another classic example of an acquisition is the Walt Disney and 21st Century Fox deal. During this time, the media landscape was rapidly changing and traditional media companies like 21st Century Fox were facing significant competition from new digital entrants like Netflix and Amazon. Fox wanted to sell their company to focus on their core strengths, primarily news and sports. 

On the other hand, Walt Disney had better content creation and distribution, which allowed them to benefit from this transaction.

Amazon and Whole Foods (2017) - $13.7B ($17B adjusted for inflation)

Though this deal did not make our top 25, it’s certainly a great example of a successful acquisition. Amazon bought Whole Foods in 2017 for approximately $13.7B to have greater control of their supply chain and broaden their reach into new markets. 

Before this deal, Amazon was more focused on e-commerce. This strategic move allowed them to expand into the brick-and-mortar grocery sector, through Whole Foods. Amazon was able to integrate its e-commerce capabilities with Whole Foods' physical store network and achieved economies of scale in several areas, especially in distribution and logistics.

Lessons from successful and failed mergers and acquisitions 

Whether it’s a success or failure, there are always lessons to be learned in the world of mergers & acquisitions. Here are some of the best lessons we want to emphasize and share.

Don’t overlook culture 

In the past, culture was one of the most underrated aspects of M&A. No one cared about it, and deal makers were only focused on the numbers and synergies. Today, practitioners are catching on, and they tend to focus more on culture during due diligence. But for those who are still not believers, you can always look up the Daimler Benz and Chrysler deal back on May 7, 1998. 

Daimler was aggressive during integration and Chrysler didn’t want to be told what to do. They didn’t get along and continued to run as separate operations. The entire deal was a disaster, which eventually led to Daimler Benz selling Chrysler to the Cerberus Capital Management firm.

Don’t take due diligence for granted

M&A teams must never take due diligence for granted and turn every possible stone. One mistake can cause massive headaches, and potentially destroy the acquiring company.  HP learned this the hard way when they acquired Autonomy back in 2011. The plan was to transform HP from a computer and printer maker into a software-focused enterprise services firm. 

The problem came after the deal was closed, and HP discovered that Autonomy was cooking the books by selling hardware at a loss to its customers while booking the sales as software licensing revenue. This is one of the most controversial deals of all time, generating massive lawsuits due to fraudulent accounting practices.

Plan for integration early in the process

The biggest mistake any practitioner could make is not planning for integration early in the M&A process. Integration is where value is created, and must be prioritized during due diligence. 

The Sprint and Nextel Communications deal back in 2005 is a great example of the importance of integration planning. The combination of these two legal entities created the third largest telecommunications provider at that time. The goal is to gain access to each other's customer bases and cross sell their product lines. 

However due to the lack of integration planning during the diligence they were not prepared for what was about to come after closing. Apparently the two companies' networks did not share the same technology and had zero overlap making integration extremely difficult. They also lost a significant amount of market share due to their clashing marketing strategies that allowed rivals to steal dissatisfied customers.

Final thoughts

Overall, it’s hard to argue which deal in US history is the most successful merger or acquisition due to the fact that sometimes the full value and potential of a deal takes years to formulate.

However, the top mergers and acquisitions take into account best practices such as robust communication, focus on the strategic goal/deal thesis, and early integration planning throughout the deal lifecycle.

Much can be learned from companies that have successfully merged with or acquired other companies.

The right technology and tools can also work to make deals more successful. The DealRoom M&A Optimization Platform aims to help teams manage their complex M&A transactions.

Whether teams need deal management software, due diligence process assistance, help with their post merger (PMI) process, or just a simple VDR, our platform provides the necessary technology and features to optimize M&A processes.