the associated ineciencies are is a prerequisite to inform any policy that will aim to accompany population growth and urban expansion in Sub-Saharan Africa. This is the purpose of this paper.

To our knowledge, our paper is the rst to provide a joint theory of customary land sales and land tenure conversion. Using a monocentric-city urban economics framework, our theoretical model studies how tenure insecurity and information asymmetry aect the conversion of land use and tenure as the city comes into shape. In our framework, all the land is initially in the hands of customary owners who practice agriculture. Intermediaries (labeled brokers) purchase land from customary owners and attempt to formalize tenure as a means to reduce tenure insecurity before reselling plots to incoming urban workers. These brokers actually encompass a variety of stakeholders who transform land and tenure, including informal brokers (known as coxers), real estate agents, developers and private individuals.<sup>2</sup> It is assumed that only brokers but not customary owners can convert tenure. This is because customary owners, who usually are agricultural laypersons, usually do not have the capacity to navigate the administration. The tenure formalization attempts of brokers, however, are not always successful, as competing claims over land ownership may emerge and derail the process before a formal property right can be established. Furthermore, land plots are heterogeneous in the probability of land tenure formalization, an assumption which reects the variety of situations that can lead to a conict (such as disputed inheritance among family members, or local disputes regarding the allocation of the plot by village customary authorities, etc.). Although brokers cannot avoid the risk of a formalization failure, they may be able to assess it to some extent. We rst analyze the case where brokers can obtain complete information on this risk. Then, their business is simply to acquire land from a customary owner and to attempt to establish statutory rights on the plot. If successful, they have to pay a conversion fee (which may cover various expenses ranging from land surveying fees to registration in the cadaster). We then contrast this with the case where brokers are unable to obtain information on the risk of a formalization failure. This is typically caused by the inherent diculty of inspecting and uncovering all dierent stakes in the ownership of a land plot. We show that brokers then face an additional problem of adverse selection as customary owners may choose to oer the riskiest plots for sale. The information asymmetry causes a land market failure, as transactions fail to take place at some specic distance from the city center.

The paper also provides a framework for an empirical analysis of land tenure conversions in Sub-Saharan African cities. It exploits a unique survey of land plots in Bamako, Mali, that were transacted between 2009 and 2012 and unbuilt at the time of 2In Mali, coxers are land brokers who facilitate transactions between customary owners and buyers. According to Durand-Lasserve et al. (2015), they maintain a network of informers in peri-urban villages to identify land that can be transacted. They negotiate with village authorities on behalf of buyers and are therefore key players in the conversion of customary agricultural land into residential land. They know how to circumvent regular procedures and deal with the administration to make sales and land tenure conversion eective. They can be found alongside roads, near plots for sale.

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