Increasing the anti-knock quality of gasoline fuels can enable higher efficiency spark ignition engines. In this study, the blending anti-knock quality of dicyclopentadiene (DCPD), a by-product of ethylene production from naphtha cracking, with various base gasoline fuels is explored. The blends were tested in an Ignition Quality Tester (IQT) and a modified Cooperative Fuels Research (CFR) engine under compression ignition (HCCI) and spark ignition modes (KLSA). These experiments allowed for the screening of DCPD’s auto-ignition characteristics across a range of combustion modes. The synergetic blending nature of DCPD was apparent and appeared to be greater than ethanol. The data presented suggests that DCPD is a potential high octane blending component in gasoline which can substitute alkylates, isomerates, reformates, or oxygenates.