From DTCC web site:
Reported estimates of the size of the credit default swap market have so far been based on surveys. These surveys tend to overstate the size of the market due to each party to a trade separately reporting its own side. Thus, when two parties to a single $10 million dollar trade each report their “side” of the trade, the amount reported is $20 million, which overstates the actual size by a factor of two since both reports relate to a single $10 million contract. When examining the outstanding amount of actual contracts registered in the Warehouse (not separately reported “sides”) as of October 9, 2008, credit default swap contracts registered in the Warehouse totaled approximately $34.8 trillion (in US Dollar equivalents). This is down significantly from the approximately $44 trillion that were registered in the Warehouse at the end of April this year.
Interesting is the size of the market Related to Mortgages:
Less than 1% of credit default swap contracts currently registered in the Warehouse relate to particular residential mortgage-backed securities. Mortgage-related index products also have some components relating to residential mortgages and, as a whole, also constitute a relatively small fraction of total credit default swaps registered in the Warehouse.