Methods are provided for processing deasphalted gas oils derived from thermally cracked resid fractions to form Group I, Group II, and/or Group III lubricant base oils. The yield of lubricant base oils (optionally also referred to as base stocks) can be increased by thermally cracking a resid fraction at an intermediate level of single pass severity relative to conventional methods. By performing thermal cracking to a partial level of conversion, compounds within a resid fraction that are beneficial for increasing both the viscosity and the viscosity index of a lubricant base oil can be retained, thus allowing for an improved yield of higher viscosity lubricant base oils from a thermally cracked resid fraction.