crude vs natural gas

crude

noun
  • Crude oil. 

  • Any substance in its natural state. 

adj
  • In a natural, untreated state. 

  • Characterized by simplicity, especially something not carefully or expertly made. 

  • Lacking tact or taste. 

  • Lacking concealing elements. 

  • Pertaining to the uninflected stem of a word. 

natural gas

noun
  • A mixture of gaseous hydrocarbons associated with petroleum deposits; mostly methane with smaller amounts of ethane, propane and butane; principally used as a fuel. 

How often have the words crude and natural gas occurred in a corpus of books? (source: Google Ngram Viewer )