Abstract: Optimizing the operation of hot oil pipelines is for the purpose of reducing energy consumption in pipelining.In this paper,a two-level hierarchical model has been developed for optimizing steady operation of hot oil pipelines,based on the decomposition principle for large systems.The hierarchical model is composed of two sub-models: a first level one to optimize the matching of pump combination with pipeline by their hydraulic characteristics,and a second level one to optimize oil temperatures in pipelining.The first level sub-model is a combinatorial optimization model,the second level sub-model is a non-linear programmmg model,and the second level has priority over the first level.As soon as a vector of oil temperature is given by the second level model,the first level model will decide the optimal matching of pump combination with pipeline under the given oil temperature,then an energy cost value (objective value) will be returned to the second level,as a measurement of energy consumption.With reference to feedbacks from the first level sub-model,the second level sub-model will decide whether the given vector is optimal or not,and if not,the vector will be updated to a new value by non-linear optimization algorithm.This process continues until an optimal solution is reached.Being conceptually valid,the two-level hierarchical model will be generally applicable to any hot oil pipeline.The program OPT01 in FORTRAN can be used to optimize steady operation of existing hot oil pipelines.and to simulate the performance of design alternatives in planning new pipelines.A numerical example with OPT01 is shown,and some discussions are made concerning the model,its algorithms and features of its optimal solution.