CBO: Financial reform bill reduces the deficit by nearly $20 billion

The estimate also includes a projected $1 billion decrease in revenues from the provisions dealing with over-the-counter derivatives over 10 years. Some taxpayers would be expected to take the position that regulated derivatives would be subject to taxes. Revenues would likely decrease because individual tax rates on short- and long-term gains and losses differ, and the timing of the taxation of gains and losses would change. 

There is "considerable uncertainty" about the size of the losses because it's also expected that the Treasury Department would issue guidance narrowly interpreting the scope and application of the tax code in regard to derivatives contracts.

CBO and JCT could not yet determine the effect of derivatives contracts provisions on federal revenues.