Professor O'Reilly is an international leader in studies of the properties and evolution of the lithosphere.using mantle-derived magmas and xenoliths. She has made major discoveries in understanding the geochemical and physical nature of the lithosphere, the evolution of its boundaries, the origin and ascent of magmas and other fluids from the mantle, the thermal structure of the continents and the processes that shape the various domains of the lithosphere in space and time.