Thermally transferred optically stimulated luminescence (TT-OSL) of quartz is the low intensity OSL measured after heating a previously optically zeroed quartz to temperatures below that erasing the OSL electron trap. We identify the source traps contributing to TT-OSL by studying the changes in TT-OSL and thermoluminescence (TL) caused by optical bleaching at various temperatures and by repeated TT-OSL measurements, and quantify source-trap parameters using the Hoogenstraaten method. We find that both the single transfer mechanism and the double transfer mechanism are contributing to TT-OSL production. Three source traps are identified when the samples are heated to 300 °C for 10 s to induce the thermal transfer. The first one corresponds to a TL peak at ∼200 °C. It captures electrons during the optical bleaching and releases these charges during subsequent heating. It provides ∼10% of the electrons that give rise to TT-OSL. The second trap corresponds to a TL peak at 290–300 °C and provides ∼80% of the electrons for TT-OSL through the single transfer mechanism. This electron trap has a depth of 1.34 ± 0.05 eV and a frequency factor in the order of 10¹¹ s⁻¹. It has a mean lifetime of 0.24 Ma at 10 °C. The third trap corresponds to a TL peak at ∼380 °C and provides ∼10% electrons for TT-OSL through the single transfer mechanism. It has a depth of 1.66 ± 0.07 eV and a frequency factor in the order of 10¹² s⁻¹. To validate the techniques used we also determined the parameters of the fast component OSL trap and received results consistent with published values. Most importantly, our results show that the relatively short lifetime of the main TT-OSL source trap limits possibilities of using TT-OSL to extend the age range of quartz OSL dating, as has been suggested by various authors.