Should you use commas?

Should you use keyword1,keyword2,keyword3 or keyword1 keyword2 keyword3 without commas?

Which is better SEO practice?

Thanks.

 

if you don't use commas the search engines will see it as one key phrase.

 

Comma is used to differentiate different keywords, otherwise it would be confusing to the SE as a looooong keyword

 

You should alway use the comma but remenber, none of the SEs look at the Meta Keyword. Many sites just leave this blank.