Thank you for your question, and welcome to Just Answer!

Unfortunately, there isn't a perfect answer to this. Images available only to Customers.

The safest strategy is to start looking around 6 months in advance so you can start comparing. You'll be able to lock in a price that you'll be happy with and won't get burned too badly.

Prices will then creep up as the date gets closer. IF there are a lot of empty seats within two weeks of the trip you can get seats for a steal. But planning your trip like this requires some flexibility and a little risk. If there aren't a lot of seats open still, you'll pay an arm and a leg.

Perhaps more important than when you purchase the tickets is what days you travel on (off peak days are cheaper), who you book it with, other packages you are including, and airfare "wars" that airlines sometimes have. Here is a nice site that includes quite a few tips of how to get the cheapest flights possible, including the tips I have listed.

http://www.ehow.com/how_111942_purchase-cheap-airline.html

Personally, if I have some flexibility I love to use Southwest airlines "Ding" program. I can fly from Oregon to New York for $89 often. Images available only to Customers.

I hope this has helped! If so, please don't forget to Accept!

Regards,

Ryan