An Improved Optimization Model for Scheduling of a Multi-Product Tree-Like Pipeline Department of Industrial Engineering, Zanjan Branch, Islamic Azad University, Zanjan, Iran Abstract In the petroleum supply chain, oil refined products are often de- livered to distribution centers by pipelines since they provide the most reliable and economical mode of transportation over large dis- tances. This paper addresses the optimal scheduling of a complex pipeline network with multiple branching lines. The main challenge is to find the optimal sequence and time of product injections/de- liveries at input /output nodes in order to satisfy product demands with minimum costs. We propose a mixed integer linear problem (MILP) approach that is capable of detecting the interface volumes in any pipeline and managing the simultaneous deliveries to distri- bution depots. Numerical examples are solved to validate the pro- posed model. Mehrnoosh Taherkhani * Received: 28 January 2019 Accepted: 20 July 2019 Keywords: Transportation Tree-like pipeline Scheduling Simultaneous injections and deliveries * Correspondence E_mail: taherkhani.mehrnoosh@gmail.com Iranian Journal of Optimization Volume 11, Issue 2, 2019, 243-259 Research Paper Islamic Azad University Rasht Branch ISSN: 2588-5723 E-ISSN:2008-5427 Online version is available on: www.ijo.iaurasht.ac.ir Iranian Journal of Optimization, 11(2), 243-259, December 2019 243