Hydroprocessing can be performed at low pressure using acoustic energy. For example, hydroprocessing a feedstock having one or more hydrocarbon compounds carried in, or mixed with, a transport gas involves flowing the feedstock through a reaction zone in a reactor that has a bulk pressure less than 68 atm and applying acoustic energy through the reaction zone. The hydrocarbon compounds are chemically reacted with a hydrogen source in the presence of a catalyst, wherein the reacting occurs in the reaction zone.