Technical Abstract: The cool-season legume grass pea, grown for both human and livestock consumption in Asia and East Africa, has some potential as gap-filling forage (late spring to early summer) in the southern Great Plains. This study was conducted to define seasonal forage production and grain yield of 10 new grass pea lines of Mediterranean origin developed by ICARDA in central Oklahoma. Three replicate sets of experimental plots (3 by 10 m) were lightly disked and fertilized with 60 kg ha-1 P2O5 during early March of 2007, 2008 and 2009. Seeds of grass pea lines 190, 288, 289, 290, 299, 387, 390, 736, B22, B111, and AC-Green fix (control) were treated with commercial liquid inoculum (Rhizobium leguminosarum) and planted at 27.5 kg ha-1 (24 cm rows) between 01 and 05 March annually. Whole plant samples were collected on four sampling dates (59, 73, 94 and 115 d after seeding), with biomass collected on the last date separated into seed and non-seed biomass. Significant (p<0.05) cultivar x sampling date interactions were observed in biomass accumulation, and significant year x cultivar interactions were observed in grain yield. All cultivars exhibited maximum biomass accumulation at early pod stage in the cultivar x sampling date interaction, with AC-Greenfix generating the most biomass (4925 kg ha-1) versus 2695(±145) kg ha-1 for 10 new Mediterranean lines across years. In the year x cultivar interaction, different groups of cultivars annually produced the most grain, with AC-Greenfix most productive in 2007 (1615 kg ha-1), lines 390, 736 and 288 in 2008 (1885, 1855, and 1750 kg ha-1, respectively) and lines B111, 736 and 190 in 2009 (1330, 1306, and 1295 kg ha-1, respectively). Additional development is required for these new Mediterranean lines to perform with the same consistency in biomass and grain production in the SGP as AC-Greenfix.