Question : Friendly URL's; Underscores to Hyphens

To date I have a number of URL's which contain underscores such as:
example.com.au/multiple_words.php

I would like to make some URL's search engine friendlier by using hyphens instead of underscores. For example:
example.com.au/multiple-words.php

URL's containing underscores are already indexed in Google, and some have been indexed for years.

1) With SEO in mind, would it be best to use redirects...
2) and what must I know if doing so?
3) At what point do I kill off page redirects?

Kindly awaiting your feedback and any other suggestions you may have related to this.

Jason

Answer : Friendly URL's; Underscores to Hyphens

Hi,

Over a year ago there was the same question asked the Google team at a conference I attended. The answer is pretty 'simple':
Google does prefer hyphens as compared to underscores, as hyphen is considered a keyword divider. However, they do not suggest changing it, once your are already using underscores. While this may seem bit contradicting info, it seems that hyphens/underscores play only minor role. The Google team confirmed they will (in the future) consider underscores and hyphens equally.
My suggestion would be: If you have a large number of pages, leave it. If you have less pages (or plenty of time) use 301 to redirect them.

Good luck.