Oil-and-gas producer Diamondback Energy suffered its worst trading session in over a year after its largest shareholder sold nearly $2 billion worth of company stock.

A filing with the Securities and Exchange Commission shows SGF Fang Holdings unloaded 9,079,675 shares for $205.26 apiece, or over $1.9 billion, on Wednesday. The transaction triggered an 8% drop in the stock price during Wednesday's session, marking its worst performance since April 2025.

SGF Fang is an investment vehicle for Lyndal Stephens Greth, the former chairwoman of Endeavor Energy Resources, which was one of the largest private oil producers in the U.S. She is also one of the world's wealthiest people: the Bloomberg Billionaires Index, where she is ranked 88th out of 500 billionaires, pegs Greth's net worth around $27 billion.

Greth assumed the role of chair at Endeavor following the death of her father, company founder Autry Stephens, in August 2024. Diamondback acquired Endeavor for roughly $26 billion in stock and cash a month later.

Large transactions through the investment vehicle, which is dedicated to holding and selling Diamondback stock, are nothing new. SGF Fang unloaded 10 million shares, amounting to roughly $2 billion, back in June; months earlier in March, the vehicle sold over 12 million shares.

Following the latest transaction, SGF Fang holds nearly 65 million company shares, worth nearly $13 billion based on Thursday's closing price of $196.94. The holdings represent an over 20% stake in the company.

Though the transactions occurred on a much smaller scale, two other Diamondback insiders sold stock a day earlier.

Teresa Dick, the company's executive vice president of accounting, sold 5,000 shares for $210 apiece on Tuesday, while Chief Legal and Administrative Officer Matt Zmigrosky shed 1,326 shares for $212.56 each. In total, the executives sold a combined $1.3 million worth of Diamondback stock.

Inside Scoop is a regular Barron's feature covering stock transactions by corporate executives and board members-so-called insiders-as well as large shareholders, politicians, and other prominent figures. Due to their insider status, these investors are required to disclose stock trades with the Securities and Exchange Commission or other regulatory groups.