Web-based group buying is practised in many businesses nowadays. Noting that the group-buying mechanism is often used with traditional selling methods, this paper develops models in which sellers provide customers with a group-buying option and a regular spot-selling option. We prove the optimality of a threshold rationing policy. Our findings help those sellers who offer multiple selling options in designing and implementing an efficient demand and inventory management system. © 2012 Elsevier B.V. All rights reserved.