Australia's banks will certainly be hoping that global bond markets quickly rebound, as they have almost A$37 billion of bonds issued in international markets, maturing over the next six months. These are The Sheet's estimates of the task and if anything probably understate the size of the refinancing challenge the banks may face, especially if market conditions don't improve. Not to mention what price they may have to pay more to roll over the debt.The refinancing task is initially evenly spread, with A$3.5 to A$4.0 billion of bonds maturing in each of the next three months. The big months are February and March next year, with maturities of more than A$14 billion and almost A$12 billion, respectively. Much of this is the 12-month debt that was hurriedly borrowed in the same months this year, although some of that debt is extendible. The bank with the greatest refinancing task is NAB, with nearly A$11 billion of bonds maturing, but Westpac is close behind with almost A$10 billion of maturities. The banks also have A$8.7 billion of bonds maturing in the domestic market, over the same period.This data has been compiled for Australia's six largest banks and Macquarie, and it needs to be viewed in the context of a known 2009 funding requirement of between A$20 to A$30 billion for each of the big four banks alone. Adding to the refinancing challenge the banks face, though, is the suggestion during the week that the Samurai bond market may have closed as a result of the failure of Lehman Bros. This would not be a surprising development, as this is a market that opens and closes on changes in investor sentiment. Yet the Australian banks have raised almost A$9 billion in debt in this market so far this year. Banks raised very little in the Samurai market in previous years.