Deregulation of the electricity industry throughout the world aims at creating a competitive market to trade electricity, which generates a host of new technical challenges to market participants and power system researchers. For transmission systems, it requires non-discriminatory open access to transmission resources. Therefore, for better transmission services support and full utilization of transmission assets, one of the major challenges is to accurately gauge the transfer capability remaining in the system for further transactions, which is termed the available transfer capability (ATC). It is crucial to develop an appropriate ATC determination methodology that enables one to evaluate the realistic transmission transfer capability by accounting for all related important requirements. This article describes the evaluation of single-area ATC using power transfer distribution factors in a combined economic emission dispatch environment. In addition, multi-area ATC is calculated with the inclusion of participation factors. Simultaneous bilateral and multilateral wheeling transactions have been carried out on IEEE 30-bus and IEEE 118-bus systems for the assessment of the ATC for both normal, line, and generator outage contingencies. The obtained ATC results are compared with the Power World Simulator to justify its accuracy. The solutions obtained are quite encouraging and useful in the present restructuring environment.