Abstract: Energy system transformation scenarios satisfying particular climate stabilization objectives, such as 2°C, suggest that a wide range of fossil energy outcomes could be consistent with such objectives. The underlying drivers of variability in these outcomes cannot, however, be easily separated. This paper attempts to shed light on such drivers using a single, state-of-the-art global integrated assessment model (GCAM) to evaluate the energy system implications of climate stabilization near 2°C. We focus specifically on the role of fossil primary energy through midcentury under different assumptions about carbon capture and storage (CCS) and bioenergy supply, as well as about the extent of end use electrification and variable renewable energy (VRE) costs. In our scenarios, coal and natural gas primary energy are most sensitive to the availability of CCS, with bioenergy supply, end use electrification and VRE costs having a secondary impact on these sources. Primary energy from coal declines by midcentury relative to 2015 in all GCAM mitigation scenarios considered here, whereas primary energy from natural gas increases by midcentury relative to 2015 in scenarios in which CCS is available but decreases in scenarios in which CCS is not available. Changes in oil primary energy by midcentury relative to 2015 are generally smaller in magnitude than changes in coal or natural gas primary energy over the same period. We explain these results in terms of fundamental energy-economic relationships and discuss the implications of these findings for broader energy policy and planning.