OSLO—Budget carrier Norwegian Air has agreed to lease up to 13 Boeing aircraft in anticipation of higher demand for travel next summer, it said on Wednesday. The lease concerns Boeing’s 737-800 NG aircraft, with delivery to begin in the fourth quarter of this year and through the first quarter of next year. Norwegian Air did not say who the lessors were but said in a statement they “are experienced and have prior relationships with Norwegian.” The planes will help deliver Norwegian’s “announced summer 2022 flying programme with flights to over 250 destinations,” it added.