How many oil tankers exist in the oceans of the world?

Answer 1

Many thousand but these differs from small "tender" rigs to huge "semi-subs".

There are only a two-three hundred semi-submersible rigs and FPSO. The drill rig here is typically 450 tons for up to 36" turrets, capable of drilling 6000m / 20 000 feet. There are no "roughnecks", all work is done by hydraulic robots that need no sleeping quarters, no rest and does not have a bad day following a weekend off. To work on these requires extensive experience in drilling and technical skills. A PhD in geology is a better qualification than strong arms.

Several answers on this sites suggest it is straight forward to get a job on these rigs.

HOWEVER:

Weight is an issue on these rigs, and the rigs are operated around the clock, usually on 12 hour on the job and 12 hours resting / stand-by. Everyone needs to eat and sleep and these quarters, add weight and complexity to the rig. So nobody that does not need to be on the rigs will be allowed to be there. If you read the report from "Deepwater Horizon" you will find that the Transocean executives that were present, they had skills and worked, beside being executives with the rig owner.