This study investigated the effect of ozonolysis on Miscanthus x giganteus, Miscanthus sinensis 'Gracillimus', Saccharum arundinaceum and Saccharum ravennae, collectively referred to as 'energy grasses'. Studies were conducted at three different ozone concentrations (40, 50 and 58 mg/l) using two ozone flow configurations - uni-directional and reversed flow. Pretreatment conditions for each variety were optimized based on lignin content and glucan recovery in ozonated solids. Results showed that ozonolysis was effective in removing up to 59.9% lignin without cellulose degradation. However, subsequent hydrolysis of pretreated solids with Celtic (R) CTec2 at 0.06 g/g raw biomass provided glucan conversion lower than untreated samples suggesting enzyme inhibition by lignin degradation products formed during ozonolysis. Future studies investigating hydrolysis efficiency of washed pretreated solids with higher enzyme loadings are therefore warranted to optimize the hydrolysis process and make it functionally feasible. (C) 2013 Elsevier Ltd. All rights reserved.