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Transmission power flows are dependent on physical laws. Transmission system expansion planning (TSEP) of a transmission utility in the deregulated environment becomes complex. It has been identified that utilities mainly perform planning to serve the needs of their own customers within a defined service territory. However, there needs to be a coordination with the neighboring transmission utilities in a proper manner. This may be for laying of inter utility lines or for laying cross territorial dedicated lines. Multiple transmission expansion plans can be obtained for any utility. Firstly, this paper introduces the concept of commonality which defines the core content of multiple plans, giving insight for identifying ranking of new lines with their relative urgency for execution. A sequence for identifying reinforcements in the transmission network under short term TSEP is then proposed. This process uses various indices based on technical studies. An illustration of the proposed approach on a modified Garver's test system is presented. Later, using the concept of “commonality” and their formulations, a coordination strategy for planning between different utilities to identify new lines for laying is developed and discussed.