Fortune has unveiled its annual ranking of the biggest revenue generators in corporate America. This year’s Fortune 500 companies represent two-thirds of the U.S. GDP, with $12 trillion in revenues, $840 billion in profits, $17 trillion in market value, and 27.9 million employees worldwide. Apple climbs to its highest rank ever at No. 3, and Walmart holds onto the No. 1 spot despite a slip in revenues, while AT&T returns to the top 10. Here are this year’s top 10 moneymakers:

1. Walmart

Fortune 500 Rank: No. 1
2015 Revenue: $482.1 billion

Walmart (WMT) is making a lot of progress in adapting its big-box approach to the 21st century and has become the second largest online retailer in the U.S. after Amazon. By giving workers raises and investing heavily in tech, its U.S. division has improved customer service and saw comparable sales rise each quarter in 2015. It is hoping to build on that with a major reset of its food business, which accounts for more than half of its sales, with a bigger focus on organic and fresh food, and by offering curbside order pick up. The retailer has also proven it can hold its own with the tech giants, rolling out Walmart Pay across the U.S. But huge challenges remain for the world’s largest company. Its e-commerce growth lags that of its main rivals. Its Sam’s Club unit is struggling to keep up with Costco. What’s more, its international division is being buffeted by a strong U.S. dollar that is eating into profits. Total sales fell for the first time in 2015.

2. Exxon Mobil

Fortune 500 Rank: No. 2
2015 Revenue: $246.2 billion

Exxon Mobil (XOM), the world’s largest publicly-traded oil and gas company by market value (China’s Sinopec and Royal Dutch Shell are larger by revenue), has ridden out the collapse in crude prices better than most, its vertically-integrated model allowing downstream businesses to capture the value that upstream operations lose when oil prices are low. ExxonMobil remains the industry benchmark for everything from profitability to safety standards, but its rocky relationship with climate change remains its Achilles’ heel. State attorneys in both New York and California have opened probes into whether it misled investors over the risks to its business from climate change, against a background of allegations (which it denies) that it suppressed scientific research that came to inconvenient conclusions.

3. Apple

Fortune 500 Rank: No. 3
2015 Revenue: $233.7 billion

After more than a decade of solid growth fueled first by the iPod music player and then by the even more popular iPhone, Apple (APPL) finally appeared to hit a wall. Still the most profitable publicly-traded company in the world, Apple’s iPhone 6S and 6S Plus upgrades barely outsold their predecessors after arriving on the market at the end of 2015, while sales of the iPad tablet computer continued to shrink throughout the year. In April 2015, the Apple Watch arrived to mixed reviews and modest sales. And though debate raged for a bit about the state of Apple’s sales in China amid a slowing economy there — including an unusual August 2015 email from CEO Tim Cook to CNBC host Jim Cramer claiming no summer slowdown — the year ended on a weak note for the company in Asia. Lately, hopes have turned to the next iPhone upgrade cycle and a push to focus on India, where Apple’s market share remains miniscule. Still, even with the growing concerns, Apple’s next big leap came into view in 2015. Dubbed Project Titan and staffed with hordes of former car industry experts, Apple’s effort to leapfrog the automobile market with an electric masterpiece likely won’t reach consumers for a few more years. But when it does, Cook and company could be riding high again.

4. Berkshire Hathaway

Fortune 500 Rank: No. 4
2015 Revenue: $210.8 billion

Warren Buffett’s insurance and investing conglomerate Berkshire Hathaway (BRKA) is less about Buffett than it ever was. The company used to generate the bulk of its income from Buffett investment mastery. But in early 2016, Berkshire completed its $32 billion acquisition of Precision Castparts. That adds to dozens of companies Berkshire now owns from car insurance company Geico, to under wear maker Fruit of the Loom, to railroad giant Burlington Northern. The company also owns, along with private equity firm 3G, a sizeable chunk of food giant Kraft Heinz. Berkshire now generates nearly three-quarters of its revenue from its non-financial, operating businesses, which is good news. As of late, Buffett’s big stock market investments like IBM and American Express haven’t looked so hot.

5. McKesson

Fortune 500 Rank: No. 5
2015 Revenue: $181.2 billion

McKesson (MCK), the largest U.S. pharmaceutical distributor, is facing some major headwinds these days. After years of strong sales growth thanks to generic drug price inflation, that tailwind is expected to slow and cut into the company’s overall revenue growth this year. McKesson also recently lost a handful of customers and could potentially lose another $13 billion worth of revenue in 2018 when (or if) Rite Aid is acquired by Walgreens. Management has been working on a series of maneuvers to lessen these blows, including acquiring strategic bolt-on companies to replace lost business and implementing a restructuring plan that’s expected to generate about $180 million in savings this fiscal year.

6. UnitedHealth Group

Fortune 500 Rank: No. 6
2015 Revenue: $157.1 billion

America’s largest health insurer UnitedHealth (UNH) had a year marked by notable departures. The company left the industry’s largest trade group, America’s Health Insurance Plans (AHIP), asserting that the association had adopted a strategy “that does not fit UnitedHealth Group and our diversified portfolio.” More recently, the company has announced that it would be leaving most of Obamacare’s statewide individual insurance marketplaces thanks to mounting losses. Both decisions speak to the insurance giant’s willingness to go it alone. That makes sense given its sheer size and the reach of its business — UnitedHealth has more than 100 million global customers. The insurer has also grown its health services platform Optum and pharmacy benefits unit OptumRx with major investments like the $12.8 billion buyout of Catamaran.

7. CVS Health

Fortune 500 Rank: No. 7
2015 Revenue: $153.3 billion

CVS Health (CVS) is still feeling the pinch from its 2014 decision to drop cigarettes. But the company continues to leverage the positive PR from that move to convince more and more employers that it is truly a health care company, allowing it to win new business for its Caremark pharmacy benefits manager. And though the PBM eclipsed its retail drugstore business size a few years ago, the company has gone full steam ahead with expanding its CVS/pharmacy business, which has been grappling with declines in comparable sales. CVS recently took over 1,700 in-store drugstores from Target and is rolling out order pickup with tech startup Curbside this year. It is also continuing to push healthier food options in its stores to burnish its image as a healthcare company and improve its beauty selection to better compete with arch-rival Walgreens.

8. General Motors

Fortune 500 Rank: No. 8
2015 Revenue: $152.4 billion

In 2015, General Motors’ (GM) most important goal was to distance itself from the ignition switch recall scandal that cast a pall over the historic brand for much of the previous year. It also had a record sales year to boot, with total global revenues of 9.8 million. For 2016, GM will look to continue staking its claim on a still growing U.S. auto market. The company is also inching towards the release of automated cars, a development that could potentially change the game for GM and the auto industry within the next decade.

9. Ford Motor

Fortune 500 Rank: No. 9
2015 Revenue: $149.6 billion

Last year Ford (F) posted its best U.S. sales performance since 2006. The newly revamped F-Series Trucks were a particularly bright spot, with more than 780,000 vehicles sold. The company will look to continue that streak as the market is expected to grow again this year, thanks to low gas prices. The company will also likely continue to push into automated driving technology to keep up with increasing competition. Ford had been in talks with technology companies like Google and Uber recently, but ultimately decided not to partner with either. CEO Mark Fields noted that company culture was a big reason for this. Fields has made a lot of noise about his commitment to growing Ford as a tech company, and that should continue as the industry continues to automate.

10. AT&T

Fortune 500 Rank: No. 10
2015 Revenue: $146.8 billion

AT&T (T) veered into a new direction in 2015 as some of its mainstay businesses ran into trouble. A continued assault from revitalized wireless carrier T-Mobile helped strip away almost two million of AT&T’s monthly mobile subscribers. And the old legacy landline phone business accelerated its decline, losing almost 10% of its revenue from the year before. So CEO Randall Stephenson made two bold gambles that may — or may not — pay off in coming years. First, he spent almost $50 billion to acquire satellite television provider DirecTV. Along with its existing cable television offering Uverse, the move immediately made AT&T one of the largest TV subscription services in the world with 26 million U.S. customers and 19 million overseas. AT&T also acquired Nextel Mexico and Iusacell for less than $5 billion. Combining the two and upgrading its Mexican infrastructure could pay off if Latin America continues to grow faster than many other parts of the world.

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