In this paper we analyse a common agency model in which agents can choose with how many principals they want to work, while principals can not condition contracts on the agent's decision to accept other contracts. In this case of "non-intrinsic" common agency we characterize the equilibrium with full agent participation. Unless the substitutability between activities performed by the agent is very strong, equilibrium activities are the same as with intrinsic common agency. However, principals

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... ffer from reciprocal competition with substitutability and the agent obtains a larger rent. On the contrary, with complementarity agent's ability to make principals compete is ineffective both for activities and informational rent. J.E.L. Classification: L140, L410, D820. * This is a substantially revised version of the Working Paper Calzolari and Scarpa (1999). We thank Paolo Bertoletti, Emanuela Carbonara and Lars Stole for helpful comments on a previous draft.