Check out the companies making the biggest moves in premarket trading:
PacWest — The regional bank popped 39% in premarket trading, adding to its nearly 82% gain on Friday. PacWest said its business is "fundamentally sound" and cut its dividend by just 1 cent per share. Western Alliance gained about 11%, while Zions Bancorp added nearly 6%.
Occidental Petroleum — The energy stock dipped less than 1% in premarket after Warren Buffett said Berkshire Hathaway doesn't plan on taking full control of the oil giant. The "Oracle of Omaha" has amassed a stake of 23.5%, while receiving approval to purchase up to 50% of the company.
Berkshire Hathaway — The conglomerate's B shares rose 1.4% in premarket after Buffett's company reported a 12.6% jump in operating earnings in the first quarter. The strong performance was driven by a rebound in the conglomerate's insurance business. Overall earnings also rose sharply thanks in part to gains in its equity portfolio, led by Apple.
Estee Lauder — Shares jumped 4.2% in premarket trading following a Sunday report from the New York Post that activist investor Nelson Peltz was contemplating a "possible shakeup" at the beauty products company. The campaign would reportedly target CEO Fabrizio Freda.
AMC — AMC shares slid 3% in the premarket after the movie theater chain said it reached an agreement to settle a shareholder class action against the conversion of AMC Preferred Equity Units into common company shares, as well as a reverse stock split. Investors approved the decision in March.
American Airlines — Shares gained about 3% in premarket trading Monday after JPMorgan upgraded the stock to overweight from neutral. Analyst Jamie Baker highlighted the company's attractive valuation and said the "Big 3" airlines — American, Delta and United — are pulling away from the broader field of providers.
Tyson Foods — Shares of the food production company tumbled 9% after Tyson cut its annual sales outlook and posted an unexpected loss for its latest quarter, according to FactSet. It also warned of a 4% decrease from the previous year in domestic beef production and flat pork production.
Viatris — Shares added 2.4% after the health-care stock topped earnings expectations and reaffirmed full-year guidance, despite a shortfall in revenue. Viatris posted $932.9 million in adjusted net income for the first quarter, ahead of the consensus estimate of $835.8 million from analysts polled by FactSet. Revenue came in at $3.72 billion against a forecast of $3.8 billion.
Fortinet — The cybersecurity company added 3.3% after being upgraded to buy from neutral by Bank of America. The Wall Street firm cited Fortinet's solid execution and strong underlying demand.
— CNBC's Yun Li, Brian Evans, Alex Harring, Sarah Min and Tanaya Macheel contributed reporting.