The present paper provides the results of tests on tall-growing perennial grass biomass suitability for use as fuel, as well as findings on the energy potential of swards and energy efficiency of biofuel production from herbaceous plants. The tests were carried out for 3 years. Eight swards differing in species composition were grown. Two of them consisted of pure rhizomatous grasses-reed canary grass (Phalaris arundinacea L.) and awnless bromegrass (Bromus inermis Leyser.)-treated with mineral fertilisers, applying N-60 split in two applications. The other swards consisted of the above-mentioned grass mixtures with legumes-sweet clover (Melilotus officinalis Lam.), perennial lupine (Lupinus polyphyllus Lindl.) and goat's rue (Galega orientalis Lam.). The mixtures did not receive nitrogen fertilisers. The soil of the experimental site is light loam with a humus content of 1.5-1.9%. The productivity of swards under good weather conditions ranged between 6.3 and 8.8 t DM ha(-1), while under adverse conditions between 2.8 and 6.5 t ha(-1). The net calorific value of dry biomass ranged from 17.1 to 18.5 MJ kg(-1) and depended on sward composition, growing conditions and cutting time. Combustion temperature ranged from 770 to 955 degrees C. In Lithuanian climatic conditions, the energy potential of tall-growing grass swards cultivated on light soils low in humus content was 115-153 GJ ha(-1), and energy input for biofuel production amounted to 8.0-19.2 GJ ha(-1). (C) 2008 Elsevier Ltd. All rights reserved.