Risk* is a simple prospect probability calculator for petroleum geoscientists. Though intended primarily as a helper application for our app Volume* — also available for free in the Android Market — it can be used standalone too.You can enter probabilities directly or use the pickers to select qualitative ‘words of estimative probability’ from Sherman Kent’s CIA protocol. The product of the probabilities is computed every time you make a new selection or touch ‘Calculate’. If you also have Volume*, the app can be launched from within that app and therefore does not need to be added to a launcher screen on your device. Once you have computed a volume, tap the new Risk* button. The volume is passed to the Risk* app, where you can enter your risk parameters, then pass P(discovery) back to Volume*.