An undiluted exhaust hydrocarbon (HC) speciation method, using flame ionization detector (FID) gas chromatographs (GC), is developed to investigate HC species from conventional and low-temperature premixed charge compression ignition (PCI) combustion, from pre- and postdiesel oxidation catalyst (DOC) exhaust. This paper expands on previously reported work by describing in detail the method and effectiveness of undiluted diesel exhaust speciation and providing a more detailed analysis of individual HC species for conventional and PCI diesel combustion processes. The details provided regarding the effectiveness of the undiluted diesel exhaust speciation method include the use of a fuel response factor (RF) for HC species quantification and demonstration of its linearity, detection limit, accuracy and precision. The listing of individual HC species provides not only the information needed to design surrogate exhaust mixtures used in reactor tests and modeling studies, but also sheds light on PCI combustion and DOC characteristics. Significantly increased engine-out concentrations of acetylene, benzene and toluene support the theory that net soot reduction associated with PCI combustion occurs due to the reduction of soot formation from soot precursors. DOC oxidation behavior differs depending on the combustion characteristics, which change exhaust species and temperature.