Two existing inventories are modified to measure motivations of DREAM mentors who volunteer as design project leaders for underrepresented, underserved high school mentees. The DREAM mentors are predominately undergraduate engineering students. Clary and Snyder's Volunteer Functions Inventory (VFI), and Esmond and Dunlop's Volunteer Motivation Inventory (VMI) are both used to determine the motivations of the mentors for volunteering. Results show that mentors are primarily motivated by the Values function, a measure of desire to help others for humanitarian reasons, independent of race, gender and experience. Returning mentors also place high value on the Understanding function, whereas new mentors are less motivated by this measure. All place some reasonably high level of importance on Reciprocity, Reactivity, and/or Recognition as measured by the VMI, suggesting the dominant motivations are purely altruistic while secondary motivations are for personal fulfillment or gain.