Do Travel website vary the fares during weekends?

Does anyone know if fares on travel websites such as travelocity, orbitz or even on the airline's website goes up during weekends/holidays as they know that people are most likely to be looking to buy tickets then?

Ryanair tells you of all its best deals in advance and has blackout periods as you say for popular days as shown on this link http://www.ryanair.com/site/EN/fares.php?dest=DUB&base=STN&pos=cday weekends are not always dearer at all just in school and public holidays .......keep checking their site to decide when you think the best deal is then book

they change prices tuesday nights