The 2,4,6-trinitrotoluene (TNT) replacement, IMX-101, containing 43.5% 2,4-dinitroanisole (DNAN), 19.7% 3-nitro-1,2,4-triazol-5-one (NTO) and 36.8% nitro-guanidine (NQ), has been certified for use as an insensitive munition. IMX-101 has passed standardized performance, stability, and aging tests but in some categories was not necessarily an improvement over TNT or RDX. This study compared the thermal stability of DNAN and another low-melting nitroarene, 2,4-dinitrotoulene (DNT). When examined individually, DNAN was more stable; but formulated in IMX-101 with NTO and NQ, the opposite was true. In two part mixtures, NQ had a similar acceleratory effect on the decomposition of both nitroarenes, while NTO had a greater impact on DNAN than on NTO. Ammonia, a reported decomposition product of both NQ and NTO, also accelerated the decomposition of both DNAN and DNT, with a larger impact on DNAN. The formation of dinitroaniline, potentially due to the interaction between the nitroarenes and ammonia, was detected by LC/MS as a decomposition product when either nitroarene was combined with NTO and/or NQ, indicating that this molecule may play a significant role in the decomposition mechanism. While not advocating the use of DNT in insensitive munitions formulations, this study addresses the importance of chemical compatibility as a criterion for selecting replacement components in formulations.