Understanding the performance of backoff algorithms in multihop ad hoc networks is a key feature to design efficient Medium Access Protocols for wireless networks. The 802.11 backoff algortihm, the Binary Exponential Backoff, and all the enhancement done to this algorithm are studied in depth in a single hop context. Very few analytical studies are done on 802.11 backoff algorithms in a multi-hop context due to the difficulty of modelling. In this paper we propose an analytical study, based on process algebra, of 4 backoff algorithms on 2 multi-hop scenarios. We evaluate the performance of each backoff algorithms from efficiency point of view and when possible from a fairness point of view.