Hydrogen is an attractive fuel for large-scale combustion systems due to its high flame speeds and clean burning characteristics. This paper presents a new set of correlations for the laminar flame speeds of hydrogen-oxygen mixtures with nitrogen (air) and helium as diluents, using a recently updated chemical kinetics mechanism. A wide excursion of equivalence ratios (phi = 0.5-5.0), pressures (1-30 atm) and temperatures (270-620 K) was performed. Flame speed correlations were developed at five pressures, namely 1, 5, 10, 20, and 30 atm for the pure-hydrogen case. The disparities between the kinetic model predictions and the correlation estimates, commonly associated with existing correlations, were significantly reduced, and the correlation estimates are within +/-13 cm/s of the model predictions. Also, a correlation for lean and high-hydrogen content (HHC) syngas blends of H-2 + CO + H2O was developed from the pure-hydrogen correlations. A wide range of pressures (1-30 atm), initial temperatures (323-550 K), steam contaminant levels (5-15%), and hydrogen content in the fuel blend (15-100%) were simulated. A design of experiments approach was adopted to determine the critical mixtures necessary to develop the correlation. The developed HHC correlation agrees within +/-12% of the model predictions. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.