The transmission usage cost allocation is one of the major issues experienced by the Electric Supply Industries. A technique is proposed which is based on graph theory for the transmission usage cost allocation to generators. The proposed impact factor is used to allocate transmission usage cost to generator based on the contributions to maximum line flows under N -1 contingency condition. For allocating the cost, Line Outage Impact Factor (LOIF) and proposed Maximum Line Outage Impact Factor (MLOIF) is used. For transmission usage cost allocation modified MW-Mile method is used. IEEE 14 bus system is used to explain the feasibility of the proposed methodology. Index Terms--Modified Kirchhoff matrix, power flow tracing, transmission pricing, transmission cost allocation.