Oil rigs were installations used to drill for and collect oil.
In the late 20th century, several companies, amongst them Hibernian Oil, maintained oil rigs off the coast of Scotland in the North Sea. Great care was taken in monitoring environmental changes to protect the rigs. Thousands of tonnes of concrete were used to create "concrete boots" on each leg of a rig.
Four rigs built by Hibernian Oil were destroyed within one month by a Skarasen, amongst them the Ben Nevis and Prince Charlie rigs. A UNIT investigation followed with the Brigadier contacting the Fourth Doctor for assistance. The Zygons were destroying the rigs to test the destructive capabilities of the Skarasen in preparation for an attack on the World Energy Conference. (TV: Terror of the Zygons)
By the 40th century, the Oil Corp had devised large, insectoid mecha oil rig vehicles which could move and drain oil on other planets after Earth's wells had dried up. Rigs were used on Boukon, which was full of oil. These rigs were armoured as piracy was common in this era. (TV: The Infinite Quest)