Building Design has released their annual ranking, The WA100, of the world’s largest architecture firms. Coming in the #1 spot (up from #2 last year) is Aecom, who, with 1,370 employees worldwide, narrowly outranked Gensler (with 1,346 employees). Completing the top three was IBI Group (1,129 employees). Aecom, Gensler, and Japanese-based firm Nikken Sekkei (ranked #4) were the top 3 earners of 2012, each making over $400 million US Dollars in Fee Income. Of the top 10 largest firms, 5 are based in North America, 3 in Asia, and 1 in the UK (Aedas, which ranked 5th, is dually based in both China and the UK). A similar trend is also evident in the list as a whole – as you can see from the graphic we compiled (after the break), US firms remain the biggest employers of architects and the highest-earners. Although the UK represents about half the number of employed architects as the US, UK firms earned almost as much in fee income. Interestingly, the only firms to grace both the Top 10 list and Building Design’s survey of the Top 5 Most Admired Firms of 2012, were Gensler (#2 Largest; #4 Most Admired) and Foster & Partners (#10 Largest; #1 Most Admired). Zaha Hadid Architects (who shared the number 5 Most Admired spot with Rogers Stirk Harbour & Partners, ranked as the 45th largest firm).