Using the universe of large Canadian manufacturing firms in 1988 and 1996, we investigate to what extent outsourcing decision can be explained by a simple property rights model. The unique availability of disaggregate information on outputs as well as inputs permits the construction of a very detailed measure of vertical integration. We also construct five different measures of technological intensity to proxy for investments that are likely to be specific to a buyer-seller relationship. A theoretical model that allows for varying degrees of investment specificity and for complementarities---an externality between buyer and supplier investments---guides the analysis. Our main findings are that (i) greater specificity makes outsourcing less likely; (ii) complementarities between the investments of the buyer and the seller are also associated with less outsourcing; (iii) property rights predictions on the link between investment intensities and optimal ownership are only supported for transactions with low complementarities. High specificity and a low risk of appropriation strengthen the predictions in the model and in the data.