Simple physics. As with oil tankers, heavy load barges and cruise ships, deep sea oil rigs float according to basic physics. As the weight of the rig pushes downwards displaced water pushes upwards, thus keeping the structure afloat.

Do oil rigs ever sink?

In early 2013, a brand new $40 million oil platform sank within few seconds during installation in the Persian Gulf. Belonging to Iran's Oil Pars Oil and Gas Company, the oil rig sank even before the workers could get a chance to escape the disaster safely.

Do oil rigs move in the water?

Before being put into place, the rig, like all other types, is towed, but this is a very slow process dependant on its size and weight. It would be rare for speeds to go above 5 knots. Semi submersible rigs are fully floating, used in waters with depths of up to 8000ft.