A Withholding Rate Pool is a group of payments made by a withholding agent to one or more recipients that have the same withholding rate. This means that the same rate of withholding tax applies to all payments in the pool. A Participating Agent Pool is a group of payments made by a participating agent to one or more recipients that have the same participating agent. Participating agents are entities that have been authorized by the IRS to act on behalf of the withholding agent to collect and remit withholding taxes.