According to one or more embodiments presently described, a feedstock oil may be processed by a method which may include hydrotreating the feedstock oil to reduce or remove one or more of sulfur content, metals content, nitrogen content, or aromatics content to produce a hydrotreated oil stream; separating at least a portion of the hydrotreated oil stream into a at least a lesser boiling point oil fraction stream and a greater boiling point oil fraction stream in a first separator; hydrocracking the greater boiling point oil fraction stream; and steam cracking the lesser boiling point oil fraction stream.