Title Operation and Flexibility Contribution of Natural Gas Tanks in Multi-carrier Energy Systems Type Article Keywords Electrical ESS, Multi-Carrier Energy System, NG Tank, Optimal Operation Abstract Energy storage systems (ESSs) have an assistive role in the operation of multi-carrier energy systems. This paper presents a type of natural gas (NG) ESS called NG tank and studies the operation and flexibility contributions of this ESS in the system. NG tank modeling and formulation are unified the same as the electrical ESS. The NG tank and the electrical ESS models are implemented on a large-scale multi-carrier energy network and the impressive effects of utilizing these units are investigated in the operational planning of the energy systems. The optimal operational problem is solved utilizing the teaching learning based optimization (TLBO) algorithm to minimize the operational cost of the system. Researchers Alireza Hamedi (First researcher) , Ali Reza Seifi (Second researcher) , Dariush Keihan Asl (Third researcher)