Carbohydrate and lignin composition of feedstock materials are major factors in determining cellulosic ethanol potential.  This study was conducted to quantify the sugars and lignin present in six potential biofuel grasses (elephantgrass, energycane, sweetcane, giant reed, giant miscanthus and sugarcane) across three sites in Florida for plant (2009) and first ratoon (2010) crops, and to calculate theoretical ethanol potential.  Biomass composition was done according to the National Renewable Energy Laboratory procedure for the determination of lignin and structural carbohydrates.  Giant miscanthus had significantly less glucose as a component of structural biomass (620 vs 680-710 mg g^-1), but significantly more minor hemicellulose sugars (41 mg g^-1 arabinose and 3.5 mg g^-1 mannose) compared to most other species.  Structural lignin concentrations varied by approximately three percentage units across species, and were generally highest in sweetcane and giant reed.  Significant variability was found among species for sugars in nonstructural extractives, but sucrose was the predominant sugar.  Sugarcane had the highest concentrations of extractive sugars, followed by energycane, then sweetcane, elephantgrass and giant reed, with giant miscanthus having the lowest concentrations of sugars as a component of extractives (150 to 750 mg g^-1).  Based on total structural and nonstructural sugars in the biomass, ethanol potentials as high as 16,500 L ha^-1 were attainable for the plant crop, and 20,900 L ha^-1 for the ratoon crop, and were comparable among sugarcane, energycane, sweetcane, and elephantgrass, but were generally less for giant reed and even less for giant miscanthus.  Overall, elephantgrass and energycane were prime candidates for cellulosic conversion due to high yields, favorable fiber characteristics and lower lignin concentrations when compared with other high yielding species.