LORIL,

A quick search led me to the following:

Air Fares - Quarterly Reports

The Consumer Air Fare Report provides information about average prices being paid by consumers in the top 1,000 domestic city pair markets in the continental United States. These markets account for approximately 70% of all domestic air travel.
http://ostpxweb.dot.gov/aviation/domfares/domfares.htm
(For contact information, see: http://ostpxweb.dot.gov/aviation/contact.htm )

For other information about air fares, please see: http://ostpxweb.dot.gov/aviation/aptcomp/aptcomp.htm http://www.dot.gov/affairs/1999/dot16399.htm http://www.dot.gov/airconsumer/bestfare.htm

This is from the FAQ section at National Transportation library:

http://ntl.bts.gov/faq/faresqtrly.html

Hope this helps.