Supplemental index is one of the two index categories (main index being the first one) where Google places certain webpages due to various flaws encountered in the indexing process.

Even though the webpage was relegated from the main index to a supplemental one, it continues to get indexed, with even fewer restrains in Google algorithm. This is the last stop for a page before is being dumped by Google.

Note that SI and Google Sandbox are two different issues; the last tends to appear after agressive backlink campaigns such as high volume on inbound links on short periods of time, disproportional with the website’s traffic, repetitive and “expensive” anchor text, anchor text changes, etc.

Also, consider that the index in which websites are included in are completely automated processes, thus there is no way of changing the index where they appear.

Primary reasons why webpages are redirected to supplemental index

1. inconsistent internal linking – the most common way a webpage ends up in the SI.

When Google performs a deep crawl of your website, it compares the site’s configuration as it was indexed on the last crawl with the new information, gathered in the current indexing operation. If there are indexed webpages that don’t show up in current site inspection, Google presumes that you dumped them. These webpages are qualified to be moved in supplemental index.

What you should do: Reinitiate a thorough internal linking campaign and put on the map all neglected webpages.

2. webpages lost their direct link from home page or main category pages.

What you should do: Easy, Get a link on the home page or category page. Check out the feedback, namely if the penalized webpage shows up in Google index.

3. webpages aren’t updated for extensive periods of time, going beyond the 12 month mark.

What you should do: rewrite the headings and the title tag. If the content is outdated, consider rewriting the entire body text. In a nutshell, focus on creating new, optimized content.

Other methods to accelerate your webpages being fetched away from Google’s Supplemental Index

> Submit your website to well rated Submission Directories. Some recommendation: Yahoo Directory, DMOZ, Best of the Web, Gimpsy and Search Sight;

> Submit press releases. Work with paid directories. These are the best: PRWeb, PRLeap, PRWeb Direct and 24-7 PR;

> Launch a backlink campaign that focuses entirely on quality. Obtain a minimum of 25 backlinks to your home page;

> Optimize your on-page factors;

One thing is for certain: webpages that are in Google’s supplemental index don’t rank well at all. If you’re in this position make sure to use what you’ve read above.