Ahead of a rumoured IPO as early as tomorrow, Facebook’s position in the ad space has been boosted by comScore data that shows its share of US ad impressions grew to 27.9% in 2011.

This is up from 21% in 2010 and means Facebook has been ranked number one in comScore’s display ad impressions category for the past three years.

Despite its well-publicised woes Yahoo is second on the list with 11% of the market, while Microsoft, Google and AOL trail with less than 5% each.

Unlike the other companies on the list Facebook is almost totally reliant on banner ads to bring in revenue.

As such it has started to place ads on almost every part of the site, including the news feed and ticker.

It claims that the ads are more effective as they are often triggered by something a user’s friends have liked or recommended.

Sources have suggested that Facebook may file the initial papers for its $100bn IPO tomorrow and there has been a slow trickle of statistics bolstering its corporate reputation in recent weeks. 

A Facebook-commissioned report from Deloitte said the social network’s economic impact is worth £12.7bn to the EU and Switzerland, supporting over 232,000 jobs.

Coupled with the comScore stats, this may help investors see potential in Facebook’s business model that justifies its predicted $100bn valuation – because at the moment its revenue doesn’t.

eMarketer estimated that Facebook would generate $4.27bn in revenue in 2011 with $3.8bn coming from advertising.

This figure is double its ad revenue from 2010 and shows impressive growth, but is still far off a $100bn valuation.