Ethiopian mustard (Brassica carinata A. Braun) is an oil-seed species that has recently become an object of great interest as a promising crop for energy purposes (biodiesel and biolubricant production). In semi-arid regions of South Italy, soil moisture at sowing time is often inadequate, delaying and reducing seed germination. In this study, the effect of reduced water potential on seed germination in three cultivars of B. carinata (ISCI 7, CT 180 and Sincron) was investigated in the laboratory. Germination behaviour at constant temperatures under low water availability was also analysed through the hydrotime model. Six water potentials (Sigma(s)) in PEG solution (0, -0.2, -0.4, -0.6, -0.8 and -1.0 MPa) and three temperatures (10, 20 and 30 degrees C) were used for the germination tests. A thermo-inhibiting effect was observed at the highest levels of water stress. The hydrotime analysis revealed that the increase of temperature to 30 degrees C reduced predicted hydrotime (theta(H)) by hastening the rate of germination, but shifted median base water potential (Sigma(b(50))) to higher values (less negative), whereas the lowering of temperature increased theta(H). These observations may have a great agronomic impact because although fewer seeds germinated at 30 degrees C at the highest levels of water stress, they may germinate faster in rapidly drying soil. However, genetic differences were observed among cultivars in terms of estimated theta(H) and Sigma(b(50)). The hydrotime modelling approach offered in this study may help predict B. carinata seed germination under soil water deficit conditions occurring under early or late autumnal sowing.