The Borana people are the predominant ethnic group on the Borana Plateau in southern Ethiopia, who have recently increased their reliance on crops. Rainfall in the region averages between 353 mm to 873 mm; variability is high, with coefficients of variation ranging from .21 to .68. Anectdotal evidence implies that the vulnerability of pastoralist households to drought is increasing; stock levels increase dramatically during good rainfall years but plummet when rainfall is poor, indicating that the drought cycle is becoming more pronounced. In recent years, there has also been a dramatic increase in land allocated to crops, and land allocated to pastures that are either privatized or accessible to only a small sub-group of people. It is hypothesized that one of the key determinants of the productivity and sustainability of the systems is the ability of community members to cooperate over the use and maintenance of these resources. In this paper, we develop indicators of cooperation and examine factors affecting these indicators. We then use these indicators to determine the impact of cooperation on stock densities and land allocation patterns. Results indicate that cooperation is positively related to factors that increase the profitability of livestock, but negatively related to the total number of households, the use of community pastures by non-community members, and heterogeneity of wealth within the community.