Sourcing grapes from independent growers for use in top quality wines sold on the international market is a major organisational challenge for corporate wineries. Our paper adds to the small existing literature addressing these coordination issues in the New World wine sector, by going deeper into the specifics of the contracts, as well as the "transaction cost economising" argument. Based on a case-study carried out in the Argentine province of Mendoza, this article presents an in-depth analysis of the technical process, in order to identify the contractual hazards posed by asset specificity, measurement costs, and non-contractible actions. Drawing on contract completion and dual sourcing literature, it analyses the contractual and non contractual mechanisms (price incentives, grower monitoring, allocation of decision rights to the winery, role of backward integration into production) used to govern such grape transactions. Through our analysis, we were able to arrive at four main conclusions. Firstly, most agreements are still verbal, with the exception of occasional written contracts, limited to a few legal provisions. It became clear to us that this approach to forging agreements is not always adequate in managing the inherently complex interactions between grape varieties, soil, farming practices and wine-making processes in high-end wine production. Secondly, extensive decision rights are allocated to wineries, to deal with incompleteness. These are key decisions to be taken during the cropping and harvesting process. Thirdly, pricing is generally kept flexible, with grape prices negotiated ex-post. This means that trade imbalances tend to be resolved in the long term. Winegrowers also benefit from financial rewards to compensate for allocations. Finally, any potential opportunistic behaviour by wineries with regards to asset specificity (in particular yield limitation) and allocation of rights is kept at bay by mechanisms such as winery reputations and credit third-party guaranty. This type of behaviour by growers is similarly deterred through monitoring and vineyard ownership on the part of the wineries.