Mediterranean summer drought conditions may limit the usefulness of most woody energy crops common in other European regions. Exotic tree species well adapted to summer stress, such as eucalyptus and acacias, may be more promising as biomass producers under such environmental conditions. Eucalypt plantations have been increasing in Portugal, for pulp and paper, over the last decades, and this species may also be considered as an option for bioenergy production. Acacias are becoming an environmental problem due to the invasive character of some species, in Portugal and other Mediterranean countries. According to the Portuguese law, they cannot be introduced anymore and the existing stands must be controlled through large scale eradication plans. The use of their wood for energy may represent an opportunity to reduce the costs of eradication. The aim of this study was the assessment of the potential of acacias to be used as a biomass-for-energy source, taking advantage of their early growth. Clonal rooted cuttings of Eucalyptus globulus were used as a reference and Acacia melanoxylon, A. pycnantha and A. dealbata, which have an invasive behaviour, were privileged as target species. They were propagated in nursery from seeds collected in the wild and a trial consisting of irrigated and rain-fed plots of each species was installed at the Instituto Superior de Agronomia (ISA) campus, in Lisbon. Survival and growth were monitored and plants were harvested 1 and 2 years after planting, sorted into biomass components, and oven-dried. Above ground dry weight was calculated on an area basis, accounting for survival. A. dealbata and A. melanoxylon had both low survival and poor biomass production, even irrigated. A. pycnantha had higher survival and biomass production than eucalypt, even in rain-fed plots, suggesting that control through biomass harvest for energy purposes may minimize eradication costs.