The US website is really not very powerful for choosing particular fares and itineraries. A reservation agent has many more options that just aren't possible on the website. This isn't really US's fault - most of the other travel websites have the same or similar restrictions.

What makes this unconscionable on the part of US is that they have a promotion that both requires the website and requires particular fares that are difficult to get the website to price.

The website basically has three options for coach fares:
1. Choose an itinerary, get the lowest coach fare.
2. Choose an itinerary, get the lowest "unrestricted" fare (available from the "more options" page. Note that the lowest unrestricted fare may not be the lowest fare that qualifies for the promotion.
3. Choose a fare, and construct an itinerary that uses that fare.

If the entire itinerary is priced using the same fare, then you *can* buy it on the website using the "search by price" option. Unfortunately you have to click on each of the rules buttons to figure out the fare basis.

This leaves out a huge number of possible itineraries that are priced using multiple different fares, but aren't the cheapest possible itineraries within the pre-defined fare classes.

If US is going to have a promotion like this, they really need to have an easy way to find cheap itineraries that qualify.