Several regional augmentation GNSS systems (like SBAS) are already fully operational and other are under development with new frequencies and signals on the way. Therefore, it becomes imperative to guarantee for all GNSS users the compatibility, interoperability and interchangeability between all these systems. The goal is to ensure that the user’s multi-mode receiver can choose and mix signals from different GNSS and SBAS systems to achieve more availability, accuracy and robustness. Attaining that objective will require agreements on frequency plans and signal designs, as well as other details including means to ensure interoperability of system times and geodetic reference systems. This paper suggests a Universal-SBAS (U-SBAS) standard, compatible with all the existing and planned regional GNSS systems (and their evolutions) in the world, like IRNSS, QZSS, PCW, BEIDOU-1, WAAS, EGNOS, SDCM, GAGAN, MSAS. The proposed worldwide multimodal U-SBAS standard carries additional channels (signals and messages) to cover the nonaeronautical specific Safety-of-Life (SoL) services, and also High Precision Positioning Services (HPPS), Position Velocity Time (PVT), authentication services, safety services, scientific application services, High Precision Timing Services (HPTS), etc. U-SBAS is designed to be fully interoperable with the current SBAS standards and to allow significant performance and service improvements in operational, scientific and/or security areas. Finally usage examples of the proposed standard are given for different types of applications such as science, aviation, precise point positioning, timing, security, robust positioning, maritime and reflectometry.