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Since travel becomes traveler and traveling in AmE (no double l), I thought that the same rule applied to propel.

However, reading and writing propeling feels awkward. (And propeler feels even more awkward...)

What is the correct spelling in American English?

(Google seems to definitely favors propelling, but I thought it best to ask the experts.)

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The same goes to "expel" and "repel". e.g. "Expeller pressed extra virgin coconut oil is your best choice." "This material is water repellent." – Elian Feb 9 '14 at 8:34
up vote 5 down vote accepted

Here are the stats from the Corpus of Contemporary American English (1990–2011) and the Corpus of Historical American English (1810s–2000s):

             COCA   COHA

propelling    425    363
propeling       0      0
propeller     782    981
propeler        0      0

The general rule, according to Wikipedia, is:

The final consonant of an English word is sometimes doubled in both American and British spelling when adding a suffix beginning with a vowel [...]. Generally, this occurs only when the word's final syllable is stressed and when it also ends with a single vowel followed by a single consonant. In British English, however, a final -l is often doubled even when the final syllable is unstressed. This exception is no longer usual in American English, apparently because of Noah Webster.

Emphasis added.

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It is worth adding that this also goes for other resonants than l: stressed program -> programmed vs. unstressed fathom -> fathomed; begin -> beginner vs. reckon -> reckoner; occur -> occurring vs. succour -> succouring. – Janus Bahs Jacquet Feb 9 '14 at 8:59

The rule as I have heard it says that AmE does not double the vowel when the syllable is unstressed. Since "propel" has final stress, that rule does not apply.

[I am not a speaker of AmE].

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