yawnmoth wrote:

I've been trying to see how changing the arrival / departure date
affects the cost of a ticket (from aa.com) and have a few questions
(all dates are 2008).

A flight from July 14th to July 17th from AUS to LHR (and vice versa)
costs $1922.00.

A flight from July 14th to July 20th from AUS to LHR (and vice versa)
costs $1375.00.

A flight from July 14th to July 21st costs $1345.00. From July 17th
to July 24th, it's $1405.00.

My question is... what's determining the prices? Why are some
flights more expensive then others?

It might be helpful to know how the fare breaks down per segment (or
direction). I would suspect there is a reason more people want to fly
from LHR to AUS on July 17, and the cheapest fares are sold out.
For the minor fare differences, some could be related to different fares
offered on different days or at different times. There might also be
some issues with some cheap fares sold out. Connecting through different
locations could also affect the price. Some fares also have minimum
stay requirements. There are a large number of reasons. Sporting
events, political events, etc.