Consider a mobile ad hoc network (MANET) where the nodes belong todifferent authorities. The nodes must be given incentives to spend theirresources (battery energy, transmission bandwidth, buffer space) inforwarding packets that originate at nodes belonging to anotherauthority. This can be done by assigning a credit balance to each node:when a node acts as an originating node it uses its credits to pay forthe costs of sending its own traffic; when a node acts as a transit nodeit earns credits by forwarding traffic from other nodes. This paperpresents a credit-based incentive scheme which assists nodes thatpersistently lack the credits necessary to transmit their data, andprotects nodes from using too large a proportion of their resources toforward traffic that originated from other nodes. We first present twobasic incentive schemes: the first scheme free-for-all does not regulatethe willingness of the nodes to forward packets on behalf of othernodes; the second scheme tit-for-tat contains such a regulatorymechanism. Next we present the origin pays and the destination paysprotocol which contain a decentralised credit redistribution mechanismto destroy (create) credit at over (under) provisioned nodes. Bothconstant and congestion-dependent resource prices are investigated.Congestion pricing is also used to reward (penalise) the destinationnode for receiving packets on under (over) utilised routes. Initialexperiments indicate that the origin pays protocol with congestionpricing offers a substantial improvement over the free-for-all protocolthat is currently used in MANETs.