methane vs propane

methane

noun
  • The simplest aliphatic hydrocarbon, CH₄, being a constituent of natural gas, and one of the most abundant greenhouse gases. 

  • Any of very many derivatives of methane. 

propane

noun
  • An aliphatic hydrocarbon, C₃H₈, a constituent of natural gas. 

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