The modeling of emitted hydrocarbons from internal combustion engines for exhaust aftertreatment devices has remained relatively unchanged since the early 1970s. This older model subdivides the hydrocarbon species into fast, slow, and non-oxidizing components. Current and future regulations from the United States Environmental Protection Agency stretch the abilities of this methodology, necessitating the need for more advanced modeling techniques. To this end, this paper provides a review on the different groups of hydrocarbons in order to provide background and contextual information on the different species expected in diesel emissions. Additionally, this work groups these species into different categories, depending on their chemical make-up, impact on human health, reactivity in the environment, and their prevalence within diesel emissions. Furthermore, this effort presents the emissions characteristics of alternative fuels by linking the feedstock source of various biodiesel fuels to the emissions produced. After understanding the different hydrocarbon emissions, a brief overview regarding the analysis of these species in the exhaust ensures that measurement of the subsequently chosen representative species is feasible. This work ends with a discussion of the choice of singular representative species for different hydrocarbon groups with the goal of improved fidelity and incorporation of biodiesel in future models.