When Warren Buffett buys or sells a stock, Wall Street and retail investors tend to pay very close attention. That's because the Oracle of Omaha's track record is virtually unsurpassed. Since taking the reins of Berkshire Hathaway (BRK.A 0.36%) (BRK.B 0.21%) in the mid-1960s, Buffett's company has averaged an annual return of 20%. This works out to an aggregate gain of greater than 2,800,000% for its Class A shares.

Although Buffett isn't perfect, he and his investing team have a knack for identifying attractively valued businesses that have clear competitive advantages. As we prepare to move into the second half of 2021, the following five Buffett stocks stand out as those that should be bought hand over fist.

Warren Buffett at his company's annual shareholder meeting.

Berkshire Hathaway CEO Warren Buffett. Image source: The Motley Fool.

Amazon

Even though Buffett's investing lieutenants, Todd Combs and Ted Weschler, are the architects behind Berkshire Hathaway's stake in Amazon (AMZN -1.11%), it's arguably the Buffett stock that should be bought most aggressively ahead of the second half of the year.

As most folks probably know, Amazon is an e-commerce juggernaut. Based on an April report from eMarketer, the company effectively controls $0.40 of every $1 spent online in the United States. It's also pivoted its online retail popularity into signing up more than 200 million people to its Prime program worldwide. The fees Amazon collects from Prime help it to undercut its competition on price. And it certainly doesn't hurt that Prime members tend to spend many multiples more than non-Prime shoppers during the course of the year.

But it's the company's cloud infrastructure service, Amazon Web Services (AWS), that has truly budded into a star. Since the operating margins associated with cloud infrastructure are considerably higher than what Amazon nets from retail and advertising, AWS' growth is leading to a surge in operating cash flow. If investors were to continue to pay the midpoint of Amazon's operating cash flow multiple over the past decade, it could hit $10,000 a share by 2025.

A lab technician using a pipette to fill test trays with liquid.

Image source: Getty Images.

Bristol Myers Squibb

Pharmaceutical stocks are money machines, and none looks to be more attractive on a valuation basis than Bristol Myers Squibb (BMY -0.87%).

One reason to be excited about this drug developer is its organic growth potential. Eliquis, which was co-developed with Pfizer, has blossomed into the world's leading oral anticoagulant, with sales expected to surpass $10 billion in 2021. Meanwhile, dozens of additional clinical trials are underway for cancer immunotherapy Opdivo, which generated $7 billion in sales last year. This offers plenty of opportunity to expand Opdivo's label and pump up its pricing power. 

Another reason Bristol Myers Squibb is such an intriguing stock is its November 2019 acquisition of cancer and immunology company Celgene. Buying Celgene brought the blockbuster multiple-myeloma drug Revlimid into the fold. Revlimid has sustainably grown its annual sales by a double-digit percentage for more than a decade, with label expansion, longer duration of use, and pricing power all playing a role. This key treatment, which topped $12 billion in sales last year, is protected from a full onslaught of generic competition until early 2026. That means Bristol Myers will be rolling in the dough for another five years, at minimum.

A smiling woman holding up a credit card with her right hand.

Image source: Getty Images.

Mastercard

Everyone seems to be looking for the smartest recovery play from the pandemic. Payment processor Mastercard (MA 0.07%) might well be the safest way to take advantage of a steady uptick in consumer and enterprise spending.

Mastercard isn't a cheap stock by any means -- at 36 times Wall Street's forward-year earnings consensus -- but it benefits from a simple numbers game. While economic contractions and recessions are inevitable, these periods of turbulence tend to be short-lived. By comparison, economic expansions often last many years. Buying into Mastercard allows investors to take full advantage of these long periods of economic expansion and robust spending. Plus, it doesn't hurt that Mastercard has the second-highest share of credit-card network purchase volume in the U.S., the leading market for consumption.

Investors can also sleep easy with the understanding that Mastercard strictly sticks to payment facilitation. Even though some of its peers also lend, and are therefore able to generate interest income and fees during bull markets, Mastercard has avoided becoming a lender. It's something you'll truly appreciate when a recession strikes. Whereas most financial stocks will be forced to set aside capital to cover credit or loan delinquencies, Mastercard won't have to. This is a big reason it bounces back from recessions quicker than most financial stocks.

Ascending stacks of generic drug tablets set atop a messy pile of one hundred dollar bills.

Image source: Getty Images.

Teva Pharmaceutical Industries

If you have an appetite for turnaround plays, brand-name and generic-drug developer Teva Pharmaceutical Industries (TEVA 0.69%) is the stock to buy hand over fist for the second half of 2021. Like Amazon, it's a stock that was added to Berkshire Hathaway's portfolio by either Combs or Weschler and not Buffett.

While there's no denying that Teva has its fair share of hurdles to overcome, the company's turnaround-focused CEO, Kare Schultz, has been a blessing. Since taking the helm less than four years ago, Schultz has helped shave off more than $10 billion in net debt, and he's overseen the reduction of roughly $3 billion in annual operating expenses. There's more work to do to improve Teva's balance sheet, but the company is very clearly on much firmer ground than it was back in 2016-2017.

Schultz also has the potential to play peacemaker for a number of outstanding lawsuits targeting Teva's role in the opioid crisis. If this litigation can be resolved with minimal cash outlay, Teva's valuation could soar. At just 4 times the company's projected earnings in 2021, Teva is about as cheap as a healthcare stock can get.

A bank teller handing cash back to a customer.

Image source: Getty Images.

Bank of America

Lastly, bank stock Bank of America (BAC 1.59%) has the look of a company that can be confidently bought hand over fist for the second half of 2021.

For much of the past decade, the Federal Reserve has kept interest rates at or near historic lows. That's meant less in the way of interest income for banks. But the latest update from the nation's central bank suggests that interest rates could begin creeping up in 2023, a year earlier than previously forecast. Bank of America is the most interest-sensitive money-center bank. According to its first-quarter investor presentation, BofA would generate $8.3 billion in net interest income on a 100-basis-point shift in the interest rate yield curve. Translation: Bank of America's profits should rocket higher beginning in 2023-2024.

At the same time, BofA has done an outstanding job of controlling its costs and improving its operating efficiency. Investments in digitization have resulted in higher mobile app and digital banking use, which is allowing the company to consolidate some of its branches. Even with its shares at a 13-year high, Bank of America has plenty left in the tank.