The work of international humanitarian organizations (IHOs) frequently involves operating in remote locations, decentralized decision-making, and the simultaneous implementation of development and disaster response programs. A large proportion of this work is funded by “earmarked” donations, since donors often exhibit a preference for the programs they are willing to fund. From extensive research involving qualitative descriptions and quantitative data, and applying system dynamics methodology, we model vehicle supply chains (VSCs) in support of humanitarian field operations. Our efforts encompass the often-overlooked decentralized environment by incorporating the three different VSC structures that IHOs operate, as well as examining the entire mix of development and disaster response programs, and the specific (and virtually unexplored) effects of earmarked funding. Our results suggest that earmarked funding causes a real—and negative—operational impact on humanitarian disaster response programs in a decentralized setting.