An experimental investigation of the primary breakup properties of round aerated-liquid jets in the annular flow regime exposed to a supersonic crossflow is described. Single- and double-pulse shadowgraphy and holography were used to study the properties of the conical liquid sheet that extends from the jet exit for finite degrees of aeration as well as the outcomes of primary breakup in the dense-spray region near the liquid jet itself The results show that the gas jet along the axis of the annular flow leaving the injector passage is underexpanded so that the excess pressure of the flow in this region forces the annular liquid sheet into a conical shape that extends from the injector exit. Primary breakup occurs in a similar manner along both the upstream and downstream sides of the liquid jet (relative to the crossflow), which suggests that there are relatively weak aerodynamic effects due to the crossflow near the jet exit. Surface velocities of the liquid sheet were measured and were used to develop correlations for the liquid sheet thickness. The sizes of ligaments and drops were measured along the liquid surface and were found to have constant diameters of 29 and 43 mu m, respectively, independent of position along the liquid sheet for the wide ranges of aeration levels, liquid/gas momentum flux ratios, injector exit passage diameters, and liquid properties considered during the present investigation. Finally, drop size distributions satisfied Simmons's universal root-normal drop size distribution function with mass median drop diameter (MMD)/Sauter mean diameter (SMD) = 1.07, which implies more nearly monodisperse drop size properties after aerated-liquid jet primary breakup than is encountered for other primary breakup processes.