Mobile network operators are currently preparing the introduction of QoS differentiation mechanisms in their 3G networks, as a means to support service-specific quality requirements, to enable the offering of distinct subscription forms and/or to enhance the resource efficiency and hence network capacity. In this paper we quantify the attainable performance and/or capacity gains from introducing different forms of QoS differentiation in an HSDPA network, considering distinct scenarios of subscription- and/or service-based differentiation. For the case of weight-based QoS differentiation, we demonstrate how the significance of the achievable performance impact and capacity gains depends on the applied differentiation weights, the traffic characteristics, the service mix and the class-specific performance requirements. For scenarios with reasonable traffic mixes and performance requirements, capacity gains of about 20 % appear very well possible. For the investigated minimum bit rate-based QoS differentiation scheme, we demonstrate an inherent trade-off between giving high-priority data users preferred access to the shared transport channel, while as a consequence reducing the spectral efficiency of the channel by granting prioritised users access even at times when their channel conditions are unfavourable. Achievable performance gains were primarily observed at cell traffic loads exceeding the 'dimensioning load', although for some scenarios capacity gains of up to 8.6 % were found, compared to a case without QoS differentiation. © 2013 Springer Science+Business Media New York.