Classification
Drilling rig construction has historically occurred in boom periods and therefore "batches" of drilling rigs have been built. Offshore drilling rigs have been classified in nominal "generations" depending upon the year built and water depth capability as follows:
| Generation | Water Depth | Dates | |
|---|---|---|---|
| First | about 600 ft | 200 m | Early 1960s |
| Second | about 1000 ft | 300 m | 1969–1974 |
| Third | about 1500 ft | 500 m | Early 1980s |
| Fourth | about 3000 ft | 1000 m | 1990s |
| Fifth | about 7500 ft | 2500 m | 1998–2004 |
| Sixth | about 10000 ft | 3000 m | 2005–2010 |
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