Here’s a friendship test: Would you share your frequent flyer miles with your pals? United Airlines is betting customers will be open to it.

The airline on Thursday started allowing members of its MileagePlus loyalty program to pool their frequent flyer miles and tap into that stash for trips on United.

A “pool leader” can pick up to four other family members or friends to participate in the joint account. The leader has to be at least 18 years old, but pool members can be any age, so families can use their children’s miles piles toward tickets.

Customers will still retain their own MileagePlus accounts and can decide how much they want to contribute to the pool. Those miles can be redeemed for flights and other products on United’s site or app.

Individuals can decide how much to contribute to the pool, and there’s a commitment: “Once those miles are in the pool …they stay in the the pool,” said Luc Bondar, chief operating officer of United’s MileagePlus loyalty program.

United isn’t the first airline to offer loyalty points pooling. JetBlue Airways lets up to seven customers pool frequent flyer miles, while Frontier Airlines allows up to eight people to pool miles. Airlines also generally allow customers to transfer miles to others, but that often comes with a fee.

“The strategy for mileage pooling is to appeal to less-frequent to moderately frequent travelers and get them and their family members engaged in the program,” said Henry Harteveldt, a travel analyst and founder of the consulting firm Atmosphere Research Group. “By allowing members of a family to pool their award points together, it increases brand preference across the family … just like with toothpaste.”