Surface energy of yellow-poplar wood from three wood treatment groups was studied using sessile-drop contact-angle measurements and the Chang acid-base model for surface energy calculation. Water, glycerol, formamide, ethylene glycol and alpha-bromonaphthalene were used as probe liquids. Wood treatments were control, hygro-thermal treatment and densification. Contact angle trends for densified and hygro-thermally treated wood were found to be the same. Total surface energy decreased with both hygro-thermal treatment and densification.