For decades, Berkshire Hathaway (NYSE:BRK.A)(NYSE:BRK.B) CEO Warren Buffett has steered his company to incredible gains. Whereas the benchmark S&P 500 has returned an extremely respectable 10% per year, inclusive of dividends, between 1965 and 2019, Berkshire Hathaway's per-share market value has grown by an average of 20.3% over the same time frame. This 10 percentage-point difference may not sound like much, but it's worked out to a greater than 2,700,000% outperformance of the S&P 500!

Even if Buffett hasn't been trouncing the market in recent years as he has in the past, Wall Street and retail investors still anxiously await the filing of Form 13F with the Securities and Exchange Commission (SEC) every three months to see what the Oracle of Omaha has been up to.

A person writing and circling the word buy underneath a dip in a stock chart.

Image source: Getty Images.

What was Warren Buffett buying during the fastest sell-off in stock market history?

Form 13F is a required filing for companies with over $100 million in assets under management, and it essentially provides a snapshot of a company's holdings as of the end of the previous quarter (in this instance, as of March 31, 2020). This means 13F filings provide insight into what Buffett and his team have been buying and selling, which is of particular importance considering the record-breaking sell-off experienced during the first quarter.

Interestingly, there wasn't nearly as much purchasing activity as selling activity. All told, 19 stocks were pared down or sold in their entirety in the first quarter. But Buffett and his team did take the opportunity to add to four names (two of which were subsequently sold in April).

A Delta Airbus A321 at an airport terminal gate.

Image source: Delta Air Lines.

Delta Air Lines

In early March, an SEC filing alerted investors that Buffett had purchased 976,507 shares of Delta Air Lines (NYSE:DAL). This close to $45 million purchase upped Berkshire's stake in Delta to almost 71.9 million shares. More importantly, it gave Berkshire a larger than 10% stake in Delta, which necessitated an SEC filing that disclosed the move. Typically, we don't find out what Buffett and his team have been up to until 13Fs are released.

The thinking at the time of the move was likely that coronavirus disease 2019 (COVID-19) fears for the airline industry would be overblown, and Delta Air Lines was, at the time, valued at a very favorable forward price-to-earnings ratio. Buffett has always been a fan of value stocks, and the more than $110 million in dividend income Delta was providing Berkshire annually was merely icing on the cake.

However, Buffett would go on to regret this move. During April, the Oracle of Omaha completely sold out of his stake in all four major airlines, including Delta. He now believes that the airline industry will be fundamentally changed by COVID-19. By this, Buffett suggests that air travel may take years to return to normal, and airlines may be forced to take on a mountain of debt that cripples their profit potential for a long time to come.

A United 737 Max 9 airplane in flight.

Image source: United Airlines.

United Airlines

Another airline stock Berkshire Hathaway added to during the first quarter was United Airlines (NASDAQ:UAL). According to the 13F, Berkshire increased its position by 218,963 shares.

Based on the $12 in earnings per share United delivered in full-year 2019, Buffett was probably enamored with the idea of picking up shares in March at between two and four times trailing 12-month earnings.

Additionally, major airlines tend to benefit when crude oil prices slump. Even before West Texas Intermediate crude fell off a cliff due to the coronavirus, oil supply was on the rise and prices were slumping. Fuel is often one of the largest expenses that airlines contend with, so a drop-off in fuel costs can really pump up their bottom lines. It also doesn't hurt that lower crude prices allow the majors like United Airlines to be more directly competitive with bare-bones regional airlines that are looking to attract passengers based on ticket price.

However, as noted, Berkshire parted ways with all of its airline stocks in April, and this included the nearly 22.2 million shares of United Airlines.

A customer speaking with a seated bank teller from across the counter.

Image source: Getty Images.

PNC Financial Services

The only true addition that still remains a holding in Berkshire Hathaway's portfolio is regional-banking giant PNC Financial Services (NYSE:PNC). Buffett and his team increased their company's stake in PNC Financial by 6%, or 526,930 shares.

Why PNC Financial? One of the biggest reasons would be value. Generally speaking, bank stocks are considered bargains when trading below their book value and potentially pricey when they surpass two times their book value. Over the past two-plus months, PNC Financial Services has been trading well below its book value, at levels Wall Street hasn't seen since 2012.

Buffett also likes to keep his ownership in bank stocks below the 10% threshold. That's because crossing this mark could lead to Berkshire Hathaway being classified as a bank holding company, which comes with a potential host of regulatory restrictions. Since Berkshire's stake in PNC Financial is still a long way away from 10%, it becomes an easy target for Buffett to add to, without having to worry about any regulatory issues.

Lastly, PNC Financial's retail banking business remained healthy in the first quarter, even with notable headwinds from the coronavirus and lower interest rates. Retail banking loans and deposits grew by a respective 8% and 5%, with the company returning a whopping $1.9 billion to shareholders through buybacks and its dividend. It checks all the boxes for a Buffett buy and hold.

A jubilant Warren Buffett at his company's annual shareholder meeting.

A jubilant Warren Buffett at his company's annual shareholder meeting. Image source: The Motley Fool.

Berkshire Hathaway

Last but not least, even though it doesn't show up in the 13F, the one stock that Buffett absolutely can't seem to get enough of lately is his own company, Berkshire Hathaway.

According to the company's first-quarter operating results, filed on May 2, Buffett and his investing team repurchased approximately $1.58 billion worth of Berkshire Hathaway stock on three separate occasions -- this includes Class A (BRK.A) and Class B (BRK.B) stock. This follows Buffett rebuying about $5 billion worth of Berkshire stock in 2019, as well as more than $1 billion in stock in 2018.

In order for Berkshire's stock to be repurchased, the company has to have more than $20 billion in cash on hand (it had $137 billion at the end of Q1), and both Buffett and right-hand man Charlie Munger have to agree that Berkshire is trading at a notable discount to its intrinsic value. Based on the repurchasing we witnessed in the first quarter and over the previous 1 1/2 years, it's pretty evident that Buffett's favorite stock right now is Berkshire Hathaway.