Low-cost airline easyJet is due to return to London's premier FTSE 100-index after a six-month absence, while British oil and gas company Ithaca Energy is due to enter the index for the first time, according to indicative data from FTSE Russell.

They will replace sports-betting and gambling group Entain and housebuilder Persimmon, according to the data.

easyJet left the index on March 23 after a two-year stint in the top flight. Its shares closed at 676 pence on Tuesday, giving the company a market value of 5.12 billion pounds ($6.99 billion). They are currently up nearly 80% over the past three months.

Aberdeen, Scotland-headquartered Ithaca Energy, which operates in the North Sea, has seen its share price climb 12% over the past three months. It has a market capitalization of 4.46 billion pounds based on its closing share price of 270 pence on Tuesday.

Entain, which houses British brands Ladbrokes and Coral, has seen its shares trade down 30% over the year to date, but up 0.4% over the past three months. It last joined the index in June 2020.

Persimmon, which last joined the index in January 2024, saw shares move down 13% over the year to date and up 7.05% over the past three months.

The expected moves are based on the companies share prices last Friday and the official announcement will be made after the market close on Wednesday, Sept. 2, based on their closing prices the day before.

The FTSE 100 is a share index of the 100 most highly-capitalized companies listed on the London Stock Exchange. Any company that falls to 111th and below is automatically ejected from the top-flight index, while any firm that rises to 90 or above is automatically promoted.

FTSE Russell is wholly owned by the London Stock Exchange Group.