This paper presents a methodology for solving the Transmission Expansion Planning Problem (TEPP) when environmental concerns are included. The traditional problem is solved minimizing the investment cost of adding transmission equipment in order to meet future demand. In this work, multiobjective approach is used to generate a set of Pareto optimal solutions from the cost and emissions standpoint as they are both conflicting objectives. The DC power flow is solved using a high order Interior Point Method (IPM), and the Elitist Non-Dominated Sorting Genetic Algorithm (NSGA-II) is used for the multiobjective problem. The methodology is tested the IEEE 24-Bus system and the Pareto optimal sets are shown for investment cost and emissions of CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> .