Accumulated frequent flier miles can be valuable assets, but what happens to those miles after someone dies? Can a spouse or other heirs inherit them, or do the miles simply evaporate like a contrail?

Whether they can be inherited depends on the airline, and in most cases, airlines will point out in their terms and conditions that frequent flier miles are not, in fact, your property. Regardless, even if the airline’s official policy is “no,” with a little perseverance, there is always the chance that the answer could be “yes.”

Here’s a look at several major airlines’ current mileage transfer rules:

Alaska Airlines’ Memorial Miles

Alaska Airlines, according to travel website and blog The Points Guy, may require only a copy of a death certificate to transfer your deceased loved one’s miles to you – without a fee. Call 1-800-654-5669 to reach Alaska Airlines customer service.

Transferring Miles With American Airlines

While current AAdvantage members do have the ability to move their miles to another member’s account (with the payment of fees and certain limitations), American Airlines will not generally allow for accrued mileage credit to be “transferable by the member upon death.” That said, the airline’s regulations do seem to offer such transfers in certain cases: “American Airlines, in its sole discretion, may credit accrued mileage to persons specifically identified in … wills upon receipt of documentation satisfactory to American Airlines and upon payment of any applicable fees.”

If your deceased loved one was an AAdvantage member, it may be worth a visit to American Airlines’ Buy, Gift, and Transfer Miles webpage to learn more.

JetBlue’s Points Pooling

In 2018, JetBlue launched the Points Pooling program to its TrueBlue loyalty members. Two to seven TrueBlue members, regardless of whether they are family, can join a “pool” and each contribute their points to it. Any member of your pool can leave their unused points for the remaining members of their pool to redeem. In theory, this would allow you to inherit the points of a loved one who passes away.

United Airlines: MileagePlus

For United Airlines customers who are part of the MileagePlus Program, it may be possible to transfer accumulated United Airlines miles upon the death of an individual.

Similar to American, the following is outlined on the airline’s website: “In the event of the death … of a Member, United may, in its sole discretion, credit all or a portion of such Member’s accrued mileage to authorized persons upon receipt of documentation satisfactory to United and payment of applicable fees.”

Call United’s customer service line at 1-800-421-4655 for guidance on the airline’s Transfer Miles Program.

Delta SkyMiles

Looking to transfer miles from a deceased Delta SkyMiles member into your name?

If you have the login details for their account, you may be able to make the transfer online via Delta’s website. Consider opening your own SkyMiles account first to simplify the process. Note that Delta charges 1¢ for each mile transferred, plus a $30 processing fee. Taxes may also apply. Miles can be transferred in 1,000-mile increments, and the maximum that can be transferred from one SkyMiles account to another is 150,000 miles per year.

Even if you have only the name of the individual and their SkyMiles number, you may still consider calling Delta’s SkyMiles customer service number at 800-323-2323 to ask for help.

Southwest Airlines

The account of a Southwest Airlines’ Rapid Rewards member who dies will become inactive and the points will be unavailable, according to the airline. In fact, its site explicitly states: “Points may not be transferred to a Member’s estate or as part of a settlement, inheritance, or will.”

Plan Ahead for Your Own Loved Ones

If you are part of an airline loyalty program and have accumulated a substantial number of miles, you may want to give your loved ones the details they need to access your frequent flier accounts so that they can log in directly in the event of your death.

Or, ask your estate planning attorney about how to go about adding into your will your wishes for passing those miles along to someone, should your preferred airline allow it.