An open ended carton including a membrane liner and a cover having a peripherally depending flange which overlies a top end portion of the carton. A transverse score line in the cover and contiguous perforation lines in the flange divide the cover into first and second sections to provide a hinged pour spout. An extension panel attached to a peripheral edge of the carton includes a terminal section which is heat sealed to an interior section of the peripheral cover flange. Severance of a hinged section of the extension panel defines an indentation between a top panel in the cover and the terminal section which receives the hinged section for locking reclosure of the cover. The cover is locked in open position by inward flexing of sections of the peripheral cover flange which are received in the carton opening.