Nowadays, transactive energy markets (TEMs) are emerging as interesting frameworks in deregulated power markets to control the balance of supply and demand in the entire electrical network. Due to wide deployment of renewable energy resources, grid connected micro-grids, and open access transmission and distribution networks, the planning and operation of TEMs become complex. So, an efficient optimal dispatch model for TEMs should be developed to achieve the objectives of TEMs, such as feasible sizes of transactions and optimal dispatch of these transactions with minimal operating costs. The transactive dispatch problem is similar to the resource allocation/matching problem. Recently, optimal transport (OT) has received significant attention in various fields including optimization theory and resource matching problems due to its potency and relevance in modeling and optimization. An OT-based approach is proposed here for optimal dispatch of transactions in energy markets while minimizing the cost of transactions considering the operating constraints of the system. The proposed approach can efficiently determine the feasible sizes of transactions without any security issues. The optimal solutions of the OT-based approach are obtained using a Sinkhorn iterative technique. Also, the load uncertainties are considered in this work to analyse the impacts of load uncertainties on the optimal dispatch of transactions. The numerical simulation results on the modified IEEE 9-bus system, modified IEEE 57-bus system, modified IEEE 118-bus system, and Indian Northern Regional Power Grid (NRPG) system illustrate the efficacy of the proposed OT-based framework.