Epidemic Routing is a data delivery scheme based on the store-carry-forward routing paradigm for sparsely populated mobile ad hoc networks. In Epidemic Routing, each node copies packets in its buffer into any other node that comes within its communication range. Although Epidemic Routing has short delay performance, it causes excessive buffer space utilization at nodes because many packet copies are disseminated over the network. In this paper, aiming at efficient buffer usage, we propose an XOR-based delivery scheme for Epidemic Routing, where nodes encode packets by XORing them when their buffers are full. Note that existing delivery schemes with coding are active coding, where source nodes always encode packets before transmitting them. On the other hand, the proposed scheme is passive coding, where source nodes encode packets only when buffer overflow would occur. Therefore, the behavior of the proposed scheme depends on the buffer utilization. More specifically, if sufficient buffer space is available, the proposed scheme delivers packets by the same operation as Epidemic Routing. Otherwise, it avoids buffer overflow by encoding packets. Simulation experiments show that the proposed scheme improves the packet delivery ratio.