Webmaster World is now running a discussion thread about what exactly are supplemental pages and some of the ways to avoid and remove them.

As the name implies, supplemental results are just that, supplemental. Google will return them only if not enough regular search results are available. In very rare chances are these results will appear on normal search query unless the keywords are very specific.

We usually know if our pages are marked as supplemental by doing a quick [site:] command.

In the following post, I am going to summarize and add my own view of why it happens, with a few suggestions on how to get out of the problem — if it is indeed an issue you can get rid of.

Why Supplemental Results Happen

What are the main causes of a page being marked as supplemental result?

• For expired domains, Google keeps a copy of the latest version of the page it crawled and display it as a Supplemental Result in the index as necessary. Usually, they are dropped after one year but may be longer.
• For a page that used to show content but now is 404, Google also keeps the lateset version of the page as it saw and display it as a Supplemental Result in the index. They also might be dropped after one year but possibly longer.
• For search that matches only on the old version, then you will see that old pages returned and marked as supplemental. Even the keywords or keyphrases are not in the cache or in live page, the returned page will highlight the search terms in the title and snippet of old version as usual.
• For duplicate content, some of the pages or URLs will appear as normal results while others will appear as Supplemental Results. This could happen because there are different links leading to multiple URLs that are duplicate ontent.
• New site which has very low inbound links or PageRank will have some of its pages in the supplemental results until the site grows up both in link popularity and age.
• Site that are hosted on unreliable hosts. When Google tries to crawl the site, the host was down.

For publishers and webmasters, this is not a good thing as pages which are supplemental obviously can not rank normally in the main index. Google explicitly marks such pages as having no or very low weight so in order for them to rank, they must get out to the main index.

Possible Solutions

Being website publishers, we could only do our best to make our sites as appealing as possible by making sure that they work flawlessly and fixing the errors if they exist.

Some of the causes of supplemental results can not be “fixed”. Still we have control over our own sites so if we are willing to work and improve the situation, their pages will eventually get into the main index.

Here are a few suggestions on how to improve affected sites:

1. Make sure that every page has only one URL that can access it. Avoid unnecessary characters after the URL. Either return 404 for other version or 301 redirect it to the only version you want to keep.
2. Decide if you want a www or non-www version of your site. Use mod_rewrite to redirect the entire domain. Google Sitemaps also has an option to choose between www or non-www to avoid duplicate content.
3. Follow best practices for a good website. Well structured pages, links, well-defined tags, etc.
4. Work on building inbound links. Get more inbound links and then more. You can never get enough of them. This will tell Google that your site and pages are important enough and get the pages our of supplemental.

Some Questions and Answers

Q: Does Google omit supplemental results in the result pages during keyword search?
A: No, but the chance of it to be included in normal search engine result pages are very slim, unless the query returns very little main results or use obscure keywords.

Q: Do supplemental URLs get re-spidered?
A: Yes, but on a less frequent schedule than URLS that are in the regular index.

Q: Are changes to supplemental URLs re-cached?
A: Because supplemental pages are also in the cache, they are also get updated.