Regular United Airlines seats appear as fare code "X," while these hidden awards appear as fare code "XN." You'll only see the hidden seats when you're logged into your United Airlines account ...

Southwest Airlines is offering 30% off many flights this summer and fall, but the deal isn't available on every ticket.

These fare class codes also apply when making flight changes. If only a higher fare class is available, you may need to pay the price difference, even when using United's same-day-change policy.