This paper addresses the coordinated operationof the electricity and natural gas networks considering theline pack flexibility in the natural gas pipelines. Theproblem is formulated as a mixed integer linear programmingproblem. The objective is to minimize the operationcost of the electricity and natural gas networks consideringthe price of the natural gas supply. Benders decompositionis used to solve the formulated problem. The masterproblem minimizes the startup and shutdown costs as wellas the operation cost of the thermal units other than the gasfiredgeneration units in the electricity network. The firstsubproblem validates the feasibility of the decisions madein the master problem in the electricity network. And ifthere is any violation, feasibility Benders cut is generatedand added to the master problem. The second subproblemensures the feasibility of the decisions of the masterproblem in the natural gas transportation network consideringthe line pack constraints. The last subproblem ensuresthe optimality of the natural gas network operation problemconsidering the demand of the gas-fired generation unitsand line pack. The nonlinear line pack and flow constraintsin the feasibility and optimality subproblems of natural gastransportation network are linearized using Newton-Raphsontechnique. The presented case study shows theeffectiveness of the proposed approach. It is shown thatleveraging the stored gas in the natural gas pipelines wouldfurther reduce the total operation cost.Keywords Benders decomposition, Line pack flexibility,Natural gas transportation network, Unit commitment