Check out which companies are making headlines before the bell:
Berkshire Hathaway – The company released its latest earnings and Warren Buffett's annual letter to investors. Berkshire's earnings were up nearly 15 percent from a year ago, and Buffett said he was still confident he could beat the overall market. Buffett appeared live on CNBC's "Squawk Box" throughout Monday morning.
Apple – Buffett revealed to CNBC's "Squawk Box" that he has personally bought more than 120 million Apple shares this year, although that was all before the company reported earnings on Jan. 31. Buffett said CEO Tim Cookhas done a "terrific" job and has done well in employing the company's capital.
Tesla – Goldman downgraded the automaker to "sell" from "neutral" on concerns about operational execution, as well as cash needs and an unproven business in its solar business, SolarCity.
Wal-Mart – Wal-Mart is running a new price-comparison test at 1,200 U.S. stores, according to a Reuters report. The idea is to close a pricing gap with domestic and international rivals, focusing on the grocery business.
Chevron – Jefferies named Chevron a "Franchise Pick," based on an analysis of the energy giant's cash flow and production growth profiles.
Urban Outfitters – MKM downgraded the apparel retailer to "sell" from "neutral" due to expected declines in sales and margins at the company's Anthropologie unit.
Boston Beer – The beer brewer also received a negative mention in Barron's, saying growing competition that has weighed on recent results are likely to continue into 2017.
Alphabet – Alphabet's Google unit will implement its digital assistant to all smartphones running the latest version of the Android operating system, not just phones made by Google.
Citigroup – Citi is being investigated over its hiring practices, according to aSecurities and Exchange Commissionfiling by the bank. The probe is focusing on whether preferential treatment was given to foreign government officials.
Sony – Sony's sales of its virtual reality headset came to just under a million in its first four months on the market. Analysts tell Reuters that pace may be too slow to spur developers to come up with new software for the PlayStation VR.
Under Armour – Under Armour was downgraded to "reduce" from "neutral" at Nomura Instinet, with the price target for the athletic apparel maker cut to $16 per share from $27. The firm feels Under Armour has moved past its high growth phase.