An empirical approach is given for specifying co-existence requirements for genetically-modified (GM) maize production, in order to ensure compliance with the 0.9% labeling threshold for food and feed in the Eur opean Union. Field data were considered in which pollen-mediated gene flow (PMGF) was measured within maize receptor fields at a series of distances from source fi elds having a marker. An empirical model is presented that fits the observed decrease of gene flow with distance. The model was parameterized to provide both reasonable worst case and expected case predictions of gene flow for various combinations of isolation distance, use of non-GM border rows in the GM field and/or separately harvested border rows in the receptor field. Based on the da ta assessed, the model is used to show that the effect of scale is minimal for source fields of surface area 4 ha and greater. Combinations of isolation distance and border rows of 20 m or more are predicted to result in gene flow of less than 0.9%, as a blen ded average for receptor fields 1 ha or larger. Lesser requirements are necessary when the source field is much smaller than the receptor.