As it is widely known, cooperation among base stations can improve spectral efficiency, particularly at cell edges. In theory, the problem is well understood, but the application of those advanced transmission techniques in practical deployments issues multiple challenges, some of which are very difficult to model in simulation studies. In this paper we investigate the properties of intra and inter-site cooperation in the cellular uplink doing practical field measurements in an urban environment. At first we concentrate on the characterization of important channel parameters which affect the performance in cooperative networks. In particular, this includes the achievable signal-to-noise ratio as well as the synchronization accuracy. Although the results show that intra-site cooperation is less complex, especially in terms of backhaul requirements and synchronization, intersite cooperation achieves (with higher probability) more balanced SNR levels at clustered base stations and, thus, higher spectral efficiency as well. This property was veryfied in the present field trial as well.