The implementation of Regional Transmission Organizations (RTOs), as encouraged in FERC Order 2000 in the United States, is requiring market based ancillary services including congestion management. This paper reviews the congestion management options being deployed in three Southeastern United States RTOs and provide details on one RTO congestion management plan. Many of the RTOs being implemented in the Southeastern USA employ firm as opposed to financial transmission rights. Firm rights offer advantages which are outlined. The congestion management practices generally employ system redispatch using ancillary services obtained from bid in markets or initially through contracts with generators. One example of the use of locational marginal pricing (LMP) is discussed as a settlement mechanism. Settlement examples are presented. The degree to which energy transactions between control areas are exposed to redispatch cost is determined by the type of transmission service reserved and probability of congestion on specific flowgates used by the transaction.