A process for decreasing fouling in a refinery unit comprising preheating a hydrocarbon feed to a refinery unit reactor zone and thereafter introducing the feed into the refinery unit reactor zone for reaction. The feed contains polymers and oligomers, and is preheated for a time and at a temperature sufficient such that when the feed is introduced into the refinery unit reaction zone for reaction, the combination of the pre-heating and heating attributable to the reaction zone causes at least 85% of the polymers and oligomers contained in the feed to unzip and wherein no more than about 5 wt % coke is formed in said feed during the preheating step.