This disclosure provides methods for separating multi-ring naphthenes from a hydrocarbon feedstock. The hydrocarbon feedstock includes at least normal paraffins, isoparaffins, 1-ring naphthenes attached with a paraffinic alkyl chain, and multi-ring naphthenes. The methods comprise passing the hydrocarbon feedstock and a solvent, at a temperature and pressure through a bed of an adsorbent comprising a metal-organic framework (MOF) adsorbent, to adsorb the multi-ring naphthenes from the hydrocarbon feedstock, thereby producing a base stock product that is depleted in multi-ring naphthenes. The metal-organic framework adsorbent is a porous crystalline material comprised of metal functionalities connected by organic linkers to form a repeating 2-D or 3-D lattice. The base stock product has a viscosity index (VI) greater than the viscosity index of the hydrocarbon feedstock. The methods of this disclosure upgrade Group II base stocks (also Group II+ base stocks) to Group III or Group III+ base stocks, and also upgrade Group III base stocks to Group III+ base stocks.