The sensitivity and performance of mixtures of HMX (octogen) and BTNNA (bis(2,2,2-trinitroethyl)nitramine) with 10-20% of ultrafine aluminum, ALEX, and other types of aluminum are studied. While the addition of aluminum results in only a small reduction of the detonation velocity, it decreases the Gurney energy of HMX much more than that of BTNNA, which is attributed to its positive oxygen balance. Formulations based on HMX and BTNNA reach top values of the Gurney velocity surpassing 3.0 mm/mus.