Separated by/with commas

[Sped Tiger]

I have been wondering which preposition is correct in this context: with or by. I think both are correct; however, I see by used more frequently than with when it comes to punctuation.
So, which is correct?
1. The phrase "in my opinion" should be separated by commas.
2. The phrase "in my opinion" should be separated with commas.

 

[Tarheel]

Separated by commas.

 

[emsr2d2]

You can't separate "a phrase" without adding something. You can separate something into two (or more) things.

The sentence should be separated, using a comma, into two phrases.
The sentence should be separated, using commas, into three phrases.

If you're splitting a sentence into two, you need one comma. If you're splitting it into more than two, you need more than one comma.

 

[Sped Tiger]

Separated by commas.

Is "with commas" wrong?

 

[White Hat]

I agree with Tarheel. Here's an example from a document released by the University of Queensland: "Each keyword is to be separated by a comma.".