What are Google supplemental results ?

Google uses two indexes for its search results. The normal index and the supplemental results index.  Unlike the main index, from which the top results of any query comes from, supplemental search results will only show up if there are very few or no results at all in the main index.

Google prevents questionable pages from being found in the main index by putting them in the supplemental index. Supplemental results are usually shown after the main search results. Pages in supplemental index are crawled less and not trusted by Google. As per Google’s definition of suppemental results

A supplemental result is just like a regular web result, except that it’s pulled from our supplemental index. We’re able to place fewer restraints on sites that we crawl for this supplemental index than we do on sites that are crawled for our main index. For example, the number of parameters in a URL might exclude a site from being crawled for inclusion in our main index; however, it could still be crawled and added to our supplemental index.

So if your pages end up in the supplemental index, it is very unlikely that your pages will show up in top ranked results for a query. 

1. １． How to find out if your web pages are in the supplemental results?

An easy way to find out how many of your pages are listed in Google’s supplemental results is to search for the following phrase on Google.com

site:www.yoururl.com ***

and proceed to the last result pages to find the supplemental results. Supplemental results will be indicated as ’supplemental’ next to the URL.

2. What kind of pages end up in Google’s supplemental results?

Any of the following factors or a combination of them can cause your pages to be in
the supplemental index.  

• Pages with very little text content.
• Pages with duplicate content.
• Pages with too many query strings in the URL (Dynamic URLs)
• Pages with same meta tags, title and description on every page.
• Pages with very few backlinks.
• Pages with very long file names with lots of dashes.
• Orphaned pages which not linked to any other pages in your site
• Pages with reciprocal links possibly to bad neighbors

Keeping these factors in mind when creating pages will help you avoid getting them in the supplemental index. Very often we see that e-commerce sites with dynamically generated URLs with many parameters often get in the supplemental index.

3. How we can get these pages out of Google’s supplemental index ?

Get some new incoming linksut some fresh content on your pages. Google indexes supplemental pages less, so the backlinks may help.

Rewrite your page title and description tags so that they are descriptive and relevant to your site, taking care that they are not too long or contain repetitive keywords.

You may need to rewrite your PHP code for e-commerce websites using mod-rewrite to simplify the cryptic URLs and also add unique meta tgs to each page.