A comprehensive numerical simulation study showed that for a typical heavy-oil reservoir, steamfold performance improves monotonically with increases in steam quality and injection rate. Hence, for this reservoir, the optimum quality and injection rate are the highest values that were investigated. In general, however, optimum steam conditions depend on reservoir type and operating mode (e.g., line drive or pattern flood). For most situations, published ＇＇rule-of-thumb＇＇ steam conditions are not optimum. Therefore, we recommend that optimum steam conditions for a specific reservoir be determined through economic comparison of predicted oil recoveries for ranges of steam conditions, as demonstrated in this study.