Soil C stocks are sensitive to changes in temperature and it is commonly believed that even minor increases in temperature may lead to large releases of C from soils to the atmosphere. Most of this thought is based on short-term incubation data and model output that implicitly assumes soil C pools are comprised of organic matter fractions with uniform temperature sensitivities. Some recent research suggests that labile and resistant soil C fractions may be equally sensitive to temperature, but other applicable research suggests that older, more resistant C fractions may be less temperature sensitive. We conducted three independent experiments to test the hypothesis that temperature sensitivity is greater for lower- than for higher-quality organic matter: parallel incubation with a newly derived method of data interpretation, temperature rises following by differing degrees of labile soil C depletion, and characterization of ¹³C derived from current and past vegetation. We found that that temperature sensitivity during the early stages of incubation is low (around 2) and increases significantly as more C is lost – we found this for a large cross-site litter decomposition experiment, for previously published soil C incubation data, and for data from our new soil C incubations. We also found that the response to a temperature rise early during soil incubation (when more labile C remained) tended to be less than that later during soil incubation (when labile C was depleted) and that older (forest-derived) soil C was significantly greater than that for younger (pasture-derived) soil C. Results from independent sources and different experiments agree that resistant soil C is more temperature-sensitive than labile soil C.