Over the last few years, mobile wireless LANs (m-WLANs), which are characterized by portable access points (APs) and a small number of connected clients, are becoming popular. When a large number of such personal mobile APs operate close to each other, for example in crowded urban areas and conference venues, the quality of service (QoS) of the connected clients can be severely degraded due to co-channel and adjacent-channel interference. While there exists a large pool of literature on interference management techniques for fixed WLANs, the small form-factor mobile APs present new challenges in terms of high-density deployments and mobility-induced dynamic interference relations. The importance of minimizing interference in m-WLANs is additionally motivated from an energy-efficiency point of view. Since mobile APs rely on limited battery power, packet collisions and retransmissions have a direct impact on the on-time of the APs. In this paper, we present results from a detailed measurement study based on commercially-available m-WLAN devices - two brands of mobile APs and smartphone based clients. While the QoS characteristics of m-WLANs operating on the same channel have been investigated in prior work, we believe this is the first study of adjacent-channel interference using real-world mobile APs. Our experiments reveal the relationship between the distance between m-WLANs and the total throughput of each m-WLAN in various combinations of channels used. Further, we outline how the results can be used for designing optimal channel allocations in dense m-WLAN settings.