** Shares of Air Transport Services Group rise 19.5% at $20.80 premarket
** Stonepeak is in advanced talks to acquire ATSG for about $3.1 bln including debt, sources told Reuters on Sunday
** The investment firm is expected to pay $22.50 per share for ATSG, representing a premium of nearly 30% to its Friday closing price
** Deal could be announced as early as Monday, sources added
** ATSG's key customers include Amazon, and co is a leading lessor of mid-sized freighters, with a fleet of 134 aircraft
** As of last close, ATSG down 1.2% YTD
(Reporting by Sukriti Gupta in Bengaluru)
((Sukriti.Gupta@thomsonreuters.com;))