A.P. Restrepo, J. Garcia-Garcia, R. Moral, F. Vidal, M.D. Pérez-Murcia, M.A. Bustamante, and C. Paredes. 2013. A comparative cost analysis for using compost derived from anaerobic digestion as a peat substitute in a commercial plant nursery. Cien. Inv. Agr. 40(2): 253-264. The aim of this study was to evaluate the economic feasibility of using compost made from anaerobically digested cattle slurries in a commercial nursery. Using a comparative cost analysis, commercial peat substrate growing media has been partially substituted with increasing proportions of compost (25, 50 and 75% v/v of compost). This experiment was intended to establish the conditions under which the use of these composts is feasible and competitive relative to commercial peat, at both agronomic and economic levels. Neither the quality of germination nor the vegetative development of the seedlings selected for the experiment (tomato, melon and pepper) were compromised, which was a necessary condition of peat substitution. In addition, the economic effects of using alternative compost media instead of peat alone have been quantified. The results showed that the most suitable scenario from an agronomic standpoint is to substitute 25% of the peat with compost because higher proportions of compost in the growing media are more limiting, especially for the tomato crop. At an economic level, reductions of up to 43% of the substrate cost and a 4.6% improvement in the commercial contribution margin for a company in this sector resulted from 50% peat substitution.