"Often" and "oftentimes"

Is there any difference between the two terms 'often' and 'oftentimes'? They seem to be used interchangeably but is one more appropriate in certain situations than others? Is 'oftentimes' an older term that is commonly replaced by 'often' nowadays?

Consider this sentence:

• Physiological tolerances can be measured indirectly by quantifying species’ occurrences along environmental axes (citation), which is often the only way such information can be recorded for large numbers of species.

• Physiological tolerances can be measured indirectly by quantifying species’ occurrences along environmental axes (citation), which is oftentimes the only way such information can be recorded for large numbers of species.

Solution 1:

Often and oftentimes may be used with little or no distinction to mean again and again in more or less close succession, but oftentimes is occasionally preferred for intonational reasons ("He had a sense of humor which was sometimes loud, oftentimes lewd, but never deliberately unkind [...].")⁽¹⁾

In the following NGRAM often is compared to oftentimes⁽²⁾.

It would seem that the use of oftentimes is very rare in written English language.

⁽¹⁾ Merriam-Webster's Dictionary of Synonyms
⁽²⁾ NGRAM is for written language only, of course.

Solution 2:

I can't find a difference in any of my online dictionaries. My best guess:

• Often is an adverb meaning frequently.
• Oftentimes is an adverb phrase-turned-word, and is similar to the adverb phrase many times. (The Oxford Dictionaries Online note that oftentimes is archaic or North American.)

In your example, then, either word is fine—you could substitute frequently or many times and see that the grammaticality of the sentence is preserved.

Usually (always?), often can replace oftentimes; however, the reverse is not true—for instance, you wouldn't say, "I don't do that oftentimes."

Solution 3:

They mean the same thing. However, "oftentimes" is colloquial and informal, and should not be used in scholarly or academic work.

Solution 4:

I have only ever heard American English speakers use "oftentimes", never British. It's not the case that "oftentimes" is exclusive to American English but it certainly appears to be more common.