The precipitation of alloy carbides in three commercial quenched and tempered martensitic steels has been studied using phase stability calculations, microscopy, microanalysis and dilatometry. The sequence of carbide stability as estimated using phase stability calculations is found to be consistent with the microstructural observations, if it is assumed that the equilibrium M23C6 phase is suppressed by kinetic considerations. One interesting result is that the molybdenum-rich phase M2C is neither predicted nor observed in any of the alloys, all of which contain substantial quantities of molybdenum. Other results include dilatometric experiments which enabled the measurement of transformation temperatures, which are compared against theoretical values.