NEW YORK (AP) — If you're flying this summer, be prepared to kiss your family goodbye at the gate. Even if they're on the same plane.

Airlines are reserving a growing number of window and aisle seats for passengers willing to pay extra. That's helping to boost revenue but also making it harder for friends and family members who don't pay this fee to sit next to each other. At the peak of the summer travel season, it might be nearly impossible.

Buying tickets two or more months in advance makes things a little easier. But passengers are increasingly finding that the only way to sit next to a spouse, child or friend is to shell out $25 or more, each way.