Multi-isotope fingerprinting of gases (methane, higher alkanes, CO 2) and of dissolved compounds in saline fluids (C, S, O, Sr, B, Li, U, Cu, Zn,…) allows for the discrimination of point contamination related to unconventional gas development compared to the environmental baseline. We present results from a multitude of settings worldwide with a focus on the identification of thermogenic stray gases from the natural background values, taking into account the prevailing redox conditions. A second aspect are the specific isotope fingerprints of flowback waters from hydraulic fracturing compared to natural saline fluids.