Constellation Energy

• 1. Introduction

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  Constellation Energy's stock lost more than half its value in a single day on the 15th of September 2008. The New York Stock Exchange halted trading. Within two days, one of the largest electricity producers in the United States was fielding a takeover bid worth billions of dollars from a subsidiary of Berkshire Hathaway. How had a company with roots stretching back to the Gas Light Company of Baltimore ended up on the edge of collapse? And how did it survive, split apart, and then come roaring back as an independent force in American energy? The answers run through nuclear power, a crisis triggered by Lehman Brothers, a decade inside one of the country's biggest utility conglomerates, and a landmark deal that will put electricity back into the reactor at Three Mile Island.

• 2. Baltimore Roots

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  Baltimore Gas and Electric created Constellation as a holding company in 1999, giving a new corporate name to a lineage that stretched back to the Gas Light Company of Baltimore. The archives that Constellation still owns tell that story: approximately 250,000 photographic prints and negatives in more than 50,000 series, held today by the Baltimore Museum of Industry. Before the 2012 merger with Exelon, Constellation Energy Group operated more than 35 power plants across 11 states, with the heaviest concentration in Maryland, Pennsylvania, New York, West Virginia, and California. The company was a Fortune 500 member and carried the NYSE ticker symbol CEG. Alongside its generation business, Constellation delivered electricity and gas to roughly two million customers spread across the continental United States, and it ranked second in local corporate giving among Baltimore-based companies, donating $7.10 million in 2017 alone.

• 3. Nuclear Ambitions

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  On the 15th of September 2005, Constellation Energy announced a joint venture called UniStar Nuclear with the French company Areva, formed specifically to market the European Pressurized Reactor in the United States. That same month three years later, the company's nuclear exposure took on a very different meaning when reports surfaced that Constellation had ties to Lehman Brothers following that firm's bankruptcy filing. The stock's 56% single-day collapse and the subsequent trading halt forced the company to hire Morgan Stanley and UBS to explore what it called "strategic alternatives." The nuclear side of Constellation's identity has since become its most defining feature. Today the company operates the United States' leading nuclear power plant fleet, with over 19,000 megawatts of capacity spread across plants in Illinois, New York, Pennsylvania, New Jersey, Maryland, and Texas. Constellation Generation Solutions, a wholly owned subsidiary, provides the maintenance and technical services that keep that fleet running. A separate subsidiary, Constellation PowerLabs, has operated since 1911 and now runs four calibrations and testing laboratories from the upper Midwest to the Northeast.

• 4. Crisis and Competing Bids

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  As Constellation's stock fell as low as $13 a share in September 2008, the company accepted an offer of $4.7 billion from MidAmerican Energy, a subsidiary of Berkshire Hathaway. Three months later it canceled that deal in favor of a $4.5 billion buyout from Electricite de France, the French state power company. That January 2009 pivot also included selling the majority of Constellation's London-based international commodities business to an affiliate of Goldman Sachs for an undisclosed price. The company had previously navigated an earlier failed merger: in December 2005, FPL Group announced a deal to acquire Constellation Energy in a transaction valued at more than $11 billion, with FPL planning to adopt the Constellation name for the combined entity. That deal was canceled on the 25th of October 2006. In July 2008, just weeks before the Lehman shock, Constellation had also purchased uranium trading firm Nufcor International from AngloGold Ashanti and FirstRand International.

• 5. Expansion Under Exelon

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  Exelon announced its intention to purchase Constellation Energy on the 28th of April 2011, and the merger closed on the 12th of March 2012. In the months between announcement and closing, Constellation was still actively building its customer base. On the 27th of May 2011 it announced the acquisition of StarTex Power, a retail electricity provider in Houston, Texas; that deal closed just days later on the 1st of June 2011. The StarTex brand was eventually discontinued in 2018. In May 2011 the company also acquired MXenergy, which served approximately half a million residential and small business customers. December 2011 brought the announced acquisition of ONEOK Energy Marketing Co., a natural gas company with customers in the Midwest. Outside the retail space, Constellation was simultaneously expanding its renewable portfolio: in April 2010 it closed an agreement with Clipper Windpower to acquire the Criterion Wind Project in Garrett County, Maryland, purchasing 28 Clipper Liberty 2.5-MW wind turbines for the site, with construction finishing in December 2010. In May 2010 it acquired two natural gas combined-cycle facilities in Texas from Houston-based Navasota Holdings for $365 million: the Colorado Bend Energy Center, a 550-MW plant near Wharton, and the Quail Run Energy Center, a 550-MW plant near Odessa, adding 1,100 MW of total capacity.

• 6. Independence and the AI Power Bet

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  In 2022, Exelon split its utilities and power generation businesses, and Constellation emerged as an independent company. Baltimore Gas and Electric remained with Exelon, but the generation portfolio went with Constellation. In September 2024, Microsoft signed a contract with Constellation to restart the undamaged nuclear reactor at Three Mile Island. In November 2025, the Trump administration committed a $1 billion federal loan to support that project. The data-center economy accelerated Constellation's next move: in January 2025, the company agreed to acquire the natural gas and geothermal power provider Calpine for $16.4 billion, or $26.6 billion when debt is included. Regulators approved the deal, and it closed in January 2026. The following month Constellation, through Calpine, entered a long-term power supply agreement with data center operator CyrusOne to deliver electricity for large-scale cloud computing and AI infrastructure. The company's venture capital arm, Constellation Technology Ventures, has also been building toward that future, with portfolio investments in companies including Proterra, ChargePoint, and Aquion Energy.