Logistics plays a crucial role in chemical supply chains. In today’s global trade environment, companies are looking for ways to lower costs in order to remain competitive. To this end, many chemical companies are increasingly outsourcing a variety of their logistics services to third-party logistics (3PL) firms in the same or other countries. This has resulted in a steady increase in the use of 3PL service-providers in the chemical sector. The objective of this paper is to model the outsourcing of various logistics services in terms of contracts offered by various 3PLs for various individual and bundled tasks. Our goal is to obtain the optimal contracts, and thus the 3PLs, that serve the total needs of the company in an integrated manner. The problem is formulated as a multi-period mixed integer linear programming (MILP) problem.