As soil organic carbon (SOC) is the largest terrestrial sink of carbon (C), sequestration of C as SOC is a potential method for climate change mitigation. Much research has been dedicated to assessing how land use change impacts SOC. These show that increasing global SOC concentrations by 0.4% to offset human C emissions is achievable. However, there is competing evidence about the factors that control the distribution of SOC and how this pool of carbon will behave under rapid climate change. Both these need to be addressed to inform potential strategies to meet these targets. This study measures SOC concentrations for a transect consisting of 12 grassland sites across Australia. These measurements are compared with rainfall, temperature, potential evapotranspiration, vegetation, elevation and soil texture. It aims to identify the major drivers of SOC distribution on a national scale and to place these observations in the context of C sequestration. Through stepwise regression methods, it was found that mean annual temperature, elevation and soil clay content were the most significant drivers of SOC distribution across the sites. These factors cannot be controlled or altered and show that, in minimally disturbed grassland systems may not have a great ability to sequester C without land use change or changes in land management. Given these ecosystems make up 30% of the Earth’s land area, this result has global implications for this climate change mitigation strategy.