The present invention concerns a buoyant fluid comprising a liquid and a
plurality of rigid containers, the rigid containers each having a sealed
void containing a gas. A particular use is to transport heavy objects
subsea. The gas in the rigid containers provides buoyancy but does not
compress at different subsea pressures. Therefore effective buoyancy
control subsea is much easier compared to known methods. For certain
embodiments, a secured supply container may be provided subsea to supply
the liquid and rigid containers to a lifting device having a container
therefor and an attachment mechanism secured to the object being
transported. The liquid is preferably a biodegradable substance such as
vegetable oil.