As a non-food, renewable energy resource, lignocellulosic biomass can be used for reducing greenhouse gas emissions. Hydrothermal carbonization (HTC) is a process to prepare the lignocellulosic biomass for subsequent thermochemical conversion. Biomass is reacted in hot compressed water at temperatures between 200 and 275 °C and at pressures sufficient to maintain liquid water. HTC was performed on corn stover, rice hulls, Tahoe mix (Jeffrey pine and white fir), switch grass, and Loblolly pine. These biomass sources encompass a variety of types, including a primary agricultural residue, a secondary agricultural residue, a forest product removed to reduce wildfires, a primary energy crop, and a primary forest crop. HTC reaction temperature was found to be the process variable with the greatest effect. For the five biomass studied, hydrochar mass yields were found to decrease with increasing reaction temperature, while higher heating values increased with increasing reaction temperature. Differences in these results among biomass sources were found to correlate with their original hemicellulose, lignin, aqueous soluble, and ash contents. These components appeared to be observable in scanning electron microscope images of hydrochar.