FILE PHOTO - Passengers check in at a counter of Delta Air Lines in Mexico City, Mexico, August 8, 2016. REUTERS/Ginnette Riquelme/File Photo

(Reuters) - Delta Air Lines Inc DAL.N said it expects a closely watched performance metric to be near the upper end of its second-quarter forecast, citing improving revenues.

Passenger unit revenue - which compares sales to flight capacity - rose about 2.5 percent in the three months ended June, the No. 2 U.S. airline said on Wednesday.

The airline had forecast passenger unit revenue to increase in the range of 1 percent to 3 percent in the quarter.

Delta also raised the lower end of its operating margin forecast to 18 percent from 17 percent, while retaining the upper end at 19 percent.

The company’s shares rose about 1 percent to $54.45 in early trading.