He narrates me a long story about the UP fares which every Airline is reluctant to offer. But if you find out how to know this UP fares then you can book your first class air ticket with less amount of money then usual. Different Airlines called this UP fares differently. Some called them as Y-UP other calls them Q-UP, M-UP, A-UP etc. Most Airlines also hide this fare from their websites. Many airlines also termed this UP fares as automatic upgrade or deeply discounted first class fares. As there is no first class code written on the ticket purchased with UP fares. So, corporate travelers benefits more whose company says NO First class.
I have browsed some Airlines websites and find out where they have hid their UP fares. I am giving you the methods to find the UP fares of three Airlines, for others you can find it for yourself by following the same techniques.
American Airlines
Finding the UP fair for American Airlines is not easy. Click on the “More Option” which is available on the search tool of their home page. Now enter your travel date and your name of the cities. Select “Fare” for the search method and click on “Business with Restrictions” option for the cabin. Lastly click on the “Action” and you will be presented with the UP fares along with other regular fares. Naturally this UP fares comes with some restrictions.

US Airways / America West
On their home page select the “One-way & Advanced Search” you will be forwarded to input-form page, write your date and name of the cities and choose the “Envoy/Business Lowest ticket type (cabin)” Lastly click on the button of “Continue Action”. You will get the result in which you will see the UP fares also.
Continental Airlines
Click on the advanced search tool which is available on their home page. You will be forwarded to the form page where you have to write your cities name and the date. Now click on the “Search Action”. You will get the result that includes the UP fares.
I hope now you must have got some idea of how to find the hidden UP fares from various Airline's homepage.
A Word of Caution
Many Airlines does not have any first class in their domestic flight. So, always make it sure that the flight you are selecting have a first class cabin before booking with UP fares.
Enjoy and do share your experiences.