Vegetation cover data, collected annually in reclaimed areas of the Syncrude and Suncor mine sites, have been analyzed to determine the effect of reclamation methods and site factors on species composition and rate of natural plant invasion. Sites monitored include reclaimed tailings sand and overburden seeded to agronomic grasses and legumes as well as sites not seeded, and reclaimed tailings sand seeded to native grasses and legumes. Natural invasion into sites seeded to agronomic grasses and legumes was minimal even after 15 years. Slightly more invasion occurred on tailings sand sites seeded to native grasses and legumes, but much more invasion occurred on non-seeded sites. Organic matter content of the surface soil layer (0 to 15 cm) had the greatest influence on the rate of invasion with the optimum soil having from 7 to 15 percent organic carbon content. There was also a trend towards more invasion on north-facing as opposed to south-facing slopes. Agronomic species, especially sweet clover, accounted for most of the invading cover in non-seeded areas. The dominant native invaders were the herbs: sow thistle, fireweed and hawksbeard. Native shrubs and trees provided negligible cover, irrespective of site factors.