Underground storage in rock caverns is widely used in Norway for many different petroleum products, such as crude oil, fuel, propane and butane. Basically, the caverns for such storages are unlined, i.e. containment is ensured without using any steel lining or membrane. The main basis for the storage technology originates from the extensive hydropower development in Norway. As part of this activity, about 4500 km of tunnels and shafts have been excavated, and around 200 large powerhouse caverns have been constructed. The hydropower tunnels are mainly unlined, with hydrostatic water pressure on unlined rock of up to 1000 m. Some of the projects also include air cushion chambers with volumes of up to 1 × 105 m3 and air pressure up to 7.7 MPa. Many lessons which are valuable also for underground oil and gas storage have been learnt from these projects. For a storage project to become successful, sys-tematic, well planned design and ground investigation procedures are crucial. The main steps of the design procedure are first to define the optimum location of the project, and then to optimize orien-tation, shape/geometry and dimensions of caverns and tunnels. As part of the procedure, ground in-vestigations have to be carried out at several steps integrated with the progress of design. The investigation and design procedures, and the great significance of these for the project to become suc-cessful will be discussed. Case examples of oil and gas storage in unlined rock caverns are given, illus-trating the relevancy of experience from high-pressure hydropower projects for planning and design of unlined caverns for oil and gas storage.