Greater competitiveness and deregulation in the sugar industry require new forms of coordination between growers and millers to increase the efficiency and profitability of the mill supply chain. This issue involves many stakeholders along the chain, with various objectives, constraints and decision-making processes. A decision support approach has been designed in order to facilitate discussion and negotiation between the stakeholders while exploring collectively satisfactory solutions. This research has been conducted in La Réunion and South Africa where millers have to deal with numerous and diverse growers. In both cases the supply chain has been described in order to determine the stakeholders' objectives, operation processes and performances regarding the cane supply from the farms to the mill. A generic conceptual model was designed and developed in an application called MAGI©. MAGI© allows one to simulate cane flows from production units to a mill, by capturing the mill supply area structure, the mill characteristics, operators' capacities along the chain, cane quantity, cane quality curves and delivery rules for each production unit. Scenarios may vary according to each of these parameters. They are compared according to the total sugar production for the season and for each production unit. This approach has been tested by comparing rearrangements of cane supply taking into account quality variations within some mill supply areas. In these cases, production units are determined as sub-areas showing similar patterns in cane quality throughout the year. Delivery rules are then modified so as to match harvest windows per production unit with quality variations between them and with capacities along the chain. Such modifications could increase total sugar production by 3% to 5%. Thus, an organisation of the harvest schedule taking into account quality differences within a mill area can give overall benefits to the mill and the growers. The approach supports di