Originally Posted by tods27

In the advanced search options (look to the left of the "Search" button), you can select Premium Economy as the class of service. This will show you options for Premium Economy (Premium Plus for UA). If you select Economy, it will show all the flights as Basic Economy (when that exists on the route), but once you select flights, you can "upgrade" to a regular Economy fare that doesn't have the BE restrictions before you purchase the ticket.