Hydrocarbon fractions boiling below 975* F. are obtained by hydrocracking heavy hydrocarbon oils, containing 40-100 percent by volume of hydrocarbon fractions boiling above 975* F., in the liquid state in the presence of ebullated catalytic macroporous microspheres. These microspheres are smaller than 60 mesh (U.S. Standard) and larger than 325 mesh. They have a pore volume of at least 0.10 cc./g. in pores larger than 250 Angstroms (A) and at least 0.30 cc./g. in pores less than 250 A. The macroporous, microspheres have an average size such that 80 weight percent fall within a narrow size range and are ebullated by the upward flow of oil and hydrogen through the reactor during hydroconversion. The pore volume of the microspheres is critical as there must be a penetration of the hydrocarbon oil into the catalyst for at least a 3 percent gain in weight.