fa Mathematical Modeling and Applications of OR Mathematical Modeling and Applications of OR پژوهشی Original <em>In this paper bus scheduling problem under the constraints that the total number of buses needed to perform all trips is known in advance and the energy level of buses is limited, is considered. Each depot has a different time processing cost. The goal of this problem is to find a minimum cost feasible schedule for buses. A mathematical formulation of the problem is developed. When there are two depots, a polynomial time algorithm is developed for the problem and theoretical results about the complexity and correctness of the algorithm is presented. Also, several examples are introduced for illustrating validity of the algorithm. </em> Bus scheduling problem, Minimum cost network flow, Polynomial time algorithm, Fixed job scheduling. 49 61 http://iors.ir/journal/browse.php?a_code=A-10-1422-3&slc_lang=fa&sid=1 M. Niksirat ملیحه نیک سیرت niksirat@birjandut.ac.ir 1111111111 1111111111 Yes Birjand University of Technology دانشگاه صنعتی بیرجند