Is it OK to have a site that has some URLs with hyphens and other, older, legacy URLs that use underscores?

[Business.com]

I'm working with a VERY large site that has recently been redesigned/recategorized. They kept only about 20% of the URLs from the legacy site, the URLs that had revenue tied to them, and these URLs use underscores. Whereas the new URLs created for the site use hyphens.

I don't think that this would be an issue for Google, as long as the pages are of quality, but I wanted to get everyone's opinion on this. Will it hurt me to have two different sets of URLs, those with using hyphens and those using underscores?

[kdaly100]

Matt Cutts video here speaks to this topic

Hope it helps...

watch?v=Q3SFVfDIS5k

[irvingw]

Absolutely not an issue, hyphens are just a little bit more SEO friendly. A lot of sites choose to leave legacy URLs when there is a chance at losing revenue by changing them. 301 redirects do lose a little bit of PR, so it makes sense to be apprehensive. It just looks less uniform.

I would suggest moving a small handful of them over and run a specific ranking report on just those URLs to monitor any loss of rank instead of moving them all in one shot and risking loss of revenue.

[PeterAlexLeigh]

Search engines handle underscores in different ways, so it's best to make them uniform and use hyphens, all being equal - This appears to be best practice in Google's eyes.

I wouldn't worry about it too much thought and I would take vitalscom's advice if you were thinking about moving them over.