derrick vs oil rig

derrick

noun
  • A framework that is constructed over a mine or oil well for the purpose of boring or lowering pipes. 

  • A device that is used for lifting and moving large objects. 

verb
  • To remove (a pitcher). 

  • To hoist with, or as if with, a derrick. 

oil rig

noun
  • A rig, consisting of platform and machinery, used to drill for oil and other petroleum products like natural gas. 

How often have the words derrick and oil rig occurred in a corpus of books? (source: Google Ngram Viewer )