This phenomenon is responsible for most regional accents in North America. Also referred to as R migration, this occurs when the letter R moves southwest across the continent. This effect is most prominent in the United States, where it causes New Englanders to "pahk" their "cahs" and Texans to "warsh" their clothes and own "erl" wells. The effect is particularly visible in Mexico and parts southern, where the R surplus is such that they must be rolled to use as many as possible per pronunciation.
Vorbis suggests that R migration occurs due to warmer climate. The theory that preferred climate of letters has to do with their position in the alphabet deserves consideration, if for no other reason than to explain why Canadians are always saying "eh".
Original idea from a contest in OMNI - original text found at http://www.phys.ufl.edu/~dunnam/ChucklesTwo.html#_Hlk438275817
Yes, Texans say "erl" instead of "oil", and I would advise anyone visiting Texas to practice not laughing uncontrollably when they hear this.
dutchess says: "When in New Orleans, I met a dog named Earl. His collar said 'Oil'."