Heavy petroleum oils such as resids are subjected to visbreaking in the presence of a hydroaromatic hydrogen donor solvent having an aromatic and alpha-to-aromatic proton content each of at least 20 percent of the total solvent hydrogen. The amount of donor solvent is from 0.1 to 50, preferably 0.1 to 20, weight percent of the heavy oil feed. The visbreaking may be carried out at relatively high severities as the use of the donor solvent reduces coke formation as well as producing a product of reduced viscosity, pour point and sedimentation characteristics. Reaction severity is usually in the range of 250 to 1500 seconds ERT at 800.degree. F. (427.degree. C.) but may range up to 15000 seconds ERT. Suitable solvents may be obtained from catalytic cracking process, for example, FCC cycle oils, slurry oils and main column bottoms.