Octane and total yield improvement in catalytic cracking

In a process for catalytic cracking of petroleum fractions having an initial boiling point of at least 400.degree. F., a 50% point of at least 500.degree. F. and an end point of at least 600.degree. F. in the presence of a conventional cracking catalyst comprising at least about 5 weight percent of a catalytically active component selected from crystalline zeolite, silica-alumina and mixtures thereof, under cracking conditions, the improvement wherein separate additive catalyst comprising a zeolite characterized by a Constraint Index of about 1 to 12 and a silica to alumina mole ratio greater than about 12 is added to said conventional cracking catalyst in the cracking process in an amount which provides the zeolite component of said separate additive catalyst at from about 0.05 weight percent to about 1.0 weight percent of the conventional cracking catalyst in the cracking process.