Data from advanced breeding experiments between 1985 and 1994 were used to determine the effects of region, year and environment on the quality of canola grown across Victoria. Estimates from these unbalanced data were made using residual maximum likelihood. Environmental effects were large relative to cultivar effects for oil and protein content, while the reverse occurred for glucosinolate content. High oil contents (and low seed protein contents) were correlated with cooler spring temperatures and higher spring rainfall. Oil contents were lowest, on average, in canola grown in dry years, or from the hotter regions, such as the Mallee, and were highest in canola from the cooler, wetter regions, such as south-western and north-eastern Victoria. Fatty acid composition varied with year and region. Means for saturated fatty acid content averaged 6.4 0.1%. The oleic acid content averaged 60.3 0.4% and was higher in canola grown in central Victoria and the Wimmera, and in most years, in north-eastern Victoria compared with other regions. Low temperatures and low rainfall reduced oleic acid content. Linoleic acid content averaged 19.7 0.3% and linolenic acid averaged 10.4 0.3%, with the content of these fatty acids negatively correlated with the content of oleic acid. Erucic acid levels were below 0.6% in all regions.