PARIS—United Airlines is boosting its fleet of Embraer E175s with a further firm order for 20 of the type, plus 19 options.

The aircraft will go to its network of United Express feeder companies, United CFO Gerry Laderman said at the Paris Air Show Monday. Including the options, the order is worth almost $2 billion at list prices.

“Think of this as an add-on to our existing fleet,” Laderman said when asked why the company was opting for the E175 E1 variant, rather than the approaching re-engined E2. “What makes this order easy is that it’s just 20 more of an aircraft we already have.” The United Express group of companies have almost 100 E175s in service at present.

The Chicago-based airline had not yet been decided to which of the United Express companies the aircraft would go, Laderman said. The option figure of 19 had been decided on as those aircraft may replace a particular existing batch of aircraft.

“I would expect these aircraft to be 70-seaters, like the E175s we’re taking this year,” Laderman added. He anticipated the aircraft would be replacements for some of the existing United Express fleet, “possibly [Bombardier] CRJ700s,” but this was not yet certain.

Embraer will start delivery of the aircraft in the second half of 2020 and expects to have delivered them all by the end of the year, Embraer Commercial Aviation CEO John Slattery said.

Asked if United had considered opting for a new type, such as the newly re-named Mitsubishi SpaceJet M100, Laderman said “I can’t say ‘never’ to any aircraft.” However, “It’s very expensive to bring in a new aircraft type,” he added.