We've initiated One WESCO, we've increased investments in our business, we've focused our execution on our top growth priorities, we've continued to aggressively develop our leaders and organizations. And we've increased the transparency of our company. This has all translated into excellent results, excellent results in the first half of 2011 that came on the heels of a very strong 2010.
As we move into the second half of 2011, we clearly have positive business momentum. Our investments are paying off, we are taking share, we've restarted our acquisition engine and we are producing very strong earnings growth. It’s our momentum and our track record of execution over the last six to eight quarters that gives us great confidence as we move through the second half of 2011.
Let's take a look at the numbers now in a little more detail. This is sales operating margin EPS and total shareholder return. On the top left is our sales results you can see that over the last four quarters we've had strong double digit sales growth, we've grown double digit sales on an aggregate roll up basis and also on an organic basis. More notably our backlog growth has exceeded our sales growth over those same four quarters. And as you will all recall our backlog is essentially project business. So it’s a good indicator, a good precursor for what portend for our construction projects going forward. The top right is our operating margin expansion, strong results. I think the takeaway is our operating model is working and our operational pullthrough is very strong.
And we had clearly talked about, that's kind of a foundational element of our business model and we are demonstrating that as move through this recovery period. Bottom left is EPS results and what we are demonstrating now I think is a track record of consistency in of meeting and beating expectations. And fundamentally on the bottom right is total shareholder return. The period that we measure here was the last six quarters. So it is from January of 2010 through the end of July 2011 and we’ve benchmarked against five key indices for us. We look at a lot more than that but I think for illustrative purposes today we picked two of the major industries, S&P 500 and Russell 2000. You can see we substantially outperformed them and three of our investment peers, Grainger, Fastenal and Anixter.