Block to Replace Hess in S&P 500 Index. Shares Jump on Admission News.

(Leon Neal/Getty Images)

Block will replace Hess in the S&P 500 index following Chevron’s purchase of Hess that closed Friday.

Block, the financial technology company formerly known as Square, will join the index before the start of trading on Wednesday, according to S&P Dow Jones Indices, which oversees the S&P 500.

Block shares are up 11% to $80.88 in after-hours trading in response to news of the S&P 500 addition which was announced around 5:15 Eastern time.

The Block addition is a mild surprise. Robinhood Markets and Applovin were prime candidates for admission into the benchmark, since they are the largest companies ranked by market capitalization that aren’t now in the index. Robinhood is valued at $93 billion, and Applovin at more than $120 billion, while Block weighs in at $43 billion.

S&P Dow Jones Indices has discretion about which companies get added to the index. There is no formula.

Write to Andrew Bary at andrew.bary@barrons.com