A gravity base structure (GBS) is a support structure held in place by gravity. A common application is for offshore oil platforms. These GBSs are often constructed in fjords since its protected area and sufficient depth is preferred for construction. GBSs intended for offshore oil platforms are constructed of steel reinforced concrete, often with tanks or cells which can be used to control the buoyancy of the finished GBS. When completed, GBSs are towed to their intended location and sunk. The platform structure which a GBS supports is called the topsides.