Multichannel wireless networks provide the flexibility to utilize the available spectrum efficiently for achieving improved system performance in terms of throughput and spectral efficiency. However, there has been no practical means for provisioning quality of service (QoS) in multichannel wireless networks. While previous proposals providing signaling and adaptation mechanisms for QoS, they support only fixed-width channels, restricting system performance in networks supporting variable-width channels. In this paper, we propose a distributed mechanism for provisioning QoS by adapting the channel widths in a multichannel, ad-hoc network. Our algorithm builds upon the well-known ETT routing metric to incorporate bandwidth adaptability. We also propose mechanisms for performing admission control and congestion control jointly in a multihop setting. We demonstrate the performance of our algorithm using a modified AODV routing protocol through extensive simulations. Our simulations results show that our proposed approach can achieve up to twice the spectral efficiency and data rates when compared to the greedy approach. Furthermore, our results show that our proposed approach scales well as the network density increases.