Turning to gross margin. 12 bips of our 50 bips improvement in the quarter came from increased delivery charges as we start to recover the higher periodic expense from higher fuel costs. The balance of the improvement primarily the result of our improving sales, pricing and purchasing disciplines, especially with our focus on migrating sales to preferred vendor and POOLCORP branded products.
Mark will cover the review of our expenses. But it's important to highlight that on a year-to-date basis, we realized an $18.5 million or 20% increase in operating income on base business sales growth of $92 million, excluding acquisitions, new location and the credit adjustments to our bad debt reserve that we had in the second quarter of 2010. Let me repeat that. On our year-to-date basis, we realized an $18.5 million increase in operating income or a 20% increase in operating income on base business sales growth of $92 million.
In terms of acquisitions and new locations, our results include the Turf Equipment Supply or TES Equipment Supply and Pool Boat acquisitions consummated late last year in the Las Vegas and Belgium markets, respectively, plus our May 2011 acquisition of certain assets from the assignee of J.L. Kilpatrick in South Florida. This last transaction enabled us to enter the South Florida Green market, the second largest market in the country. Combined, these acquisition added 8 location store network. In addition, we have also opened 3 centers in 2011, 2 in Florida and 1 in Puerto Rico.