We consider an online, processor sharing system with a single server in a packet-switched network where the processor multiplexes packets from multiple input ports onto the same output link. Under a fluid model, in which incoming data is treated as infinitely divisible, the multiplexer allocates its output capacity to serve fractions of packets from all input ports simultaneously (which we call a fluid policy). However, due to the packet nature of the network traffic, a multiplexer scheduler must approximate this fluid policy by a schedule in which only whole packets are sent (which we call a packetized policy). We assume that at each time instant, the aggregate service rate demanded by a fluid policy is no greater than the output link capacity. Then, for a single server with N input ports, and a scheduler using speedup s of at least 2 and a lookahead window of L/spl ges/0 time steps, we prove bounds on worst-case maximum additional delay D. In particular, we show that ([Ne/sup -s/]-L-2)/sup +//spl les/D min {([Ne/sup 1-s/]-L)/sup +/, [Ne/sup -s/]}. In the case when no lookahead is used (L=0), a tighter bound can be obtained: ([Ne/sup -s/]-2)/sup +//spl les/D/spl les/[Ne/sup -s/}.