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Genotype × environment interaction (GE) is a perennial problem in plant breeding and must be dealt with. Dealing with GE starts with differentiation of repeatable GE from unrepeatable GE in a target region. Repeatable GE can be used by dividing the target region into mega‐environments (MEs) and breeding ME‐specific cultivars, and unrepeatable GE must be accommodated by testing adequately within a ME. This study applied LG (location‐grouping) biplot analysis to several datasets from multiyear oat (Avena sativa L.) variety trials conducted at locations across Canada. Analysis showed that the oat growing regions in Canada can be divided into three MEs: the crown rust (Puccinia coronata Corda f. sp. avenae Eriks.) prone regions in southern and eastern Ontario (ME1), other regions in eastern Canada (ME2), and the Canadian Prairies (ME3). In addition, two sub‐MEs existed within ME2. Latitude was shown to be the main factor for the ME differentiation. The results suggest that oat variety trials should be conducted and cultivar recommendation be made according to MEs, as opposed to by administrative regions that are currently in place. [ABSTRACT FROM AUTHOR]