text: Im sorry I've not got the sources for this but I've had experience on several rigs. For a start there are two main kinds of rigs.  \n\nFor drilling a mobile rig is usually used (cos theres no garuntee of oil!). This is usually a large floating structure which is held in place with anchors. Barges carefully transport the massive anchors about 3-4km away then they're dropped and winched in until the line is taught. Were talking 20-30 ton anchors and 4 inch thick cable. The anchors have to be in a close to perfect triangle/square as possible.\n\nThis rig will drill down, hopefully strike oil and cap the well.  \n\nThen a production rig will be moved into that place.  The most common technique these days is to have a huge hollow metal cylinder, capped at each end (i cant remember the design name, help me!) about 100-150m long 20-50m wide. This is dragged out to sea then pumped with water until it stands slightly above the surface. Its amazingly stable and can deflect strong currents.(some dynamics principals I can't remember). All the production lines are protected very well inside the cylinder. Sometimes anchorage is used but its rarely neccessary.  \n\nThe production unit/platform is then neatly plonked ontop of the cylinder. \n\nIn the olden days most offshore oil was close enough to the surface you could built a structure from the sea bed up. This almost never happens anymore.\n\nSorry I can't be more precise!