Abstract: Methods and apparatus for refining feedstocks, such as crude or synthetic oil, and like feedstocks, are disclosed herein. In some embodiments, a reactor for refining a feedstock includes: a chamber having an inner volume to hold a liquid feedstock, a feedstock inlet port, a process gas inlet port, and an outlet port; a gas diffuser housed within the chamber and coupled to the process gas inlet port; and a radical generator coupled in fluid communication with the inner volume via the gas diffuser. In some embodiments, a method for refining feedstock includes: providing liquid feedstock to an inner volume of a reactor; flowing a radicalized process gas from a radical generator into the inner volume and into contact with the feedstock via a gas diffuser to fractionate the feedstock and produce one or more fractions of product in a vaporous mixture; and collecting a desired product from the vaporous mixture.