United and Delta have adopted major changes to their loyalty reward programs that experts say will benefit the airlines at the expense of passengers. But program members don't know of them, a survey found.

Starting Jan. 1, Delta's SkyMiles program was overhauled to offer reward miles based on money spent instead of miles flown. United's MileagePlus program switched to a similar system March 1.

Now, high-paying fliers earn more points than passengers in the economy section of the same flight. But a MileCards.com survey found that two-thirds of fliers didn't know of the changes.