Please recognize that today's discussion contains forward-looking statements. Actual results could differ materially from management's current expectations and plans. The company undertakes no obligation to publicly update or revise any forward-looking statements. Please review the cautionary statements in the earnings release in our most recent 10-Q.
And now with that, let me turn it over to Mike Polk for his comments.
Michael B. Polk
Thank you, Nancy. Good morning, everyone, and thanks for joining us. My objective today is twofold. First, I'll review our fourth quarter and full year results and share some observations about our performance. Second, I'll explain our thinking about 2012 and provide guidance for the year.
Let's get into the results. We posted a solid Q4, delivering 3.7% core sales growth. Q4 was the strongest quarter of the year, driving second half core sales growth to 3.5% and full year core growth to 1.8%, versus our guidance range of 1% to 3%. Reported sales in Q4 were also up 3.7%, resulting in full year reported sales growth of 3.6%. Q4 normalized EPS was $0.40, resulting in a full year normalized EPS of $1.59, up 6% versus prior year and in the middle of our guidance range of $1.55 to $1.62. While our effective tax rate was substantially higher than prior year in Q4, we did benefit from a better rate than expected. This benefit was driven by improved European profitability, which enabled us to access more NOLs than we had anticipated.
In Q4, we delivered 150 basis points of operating margin expansion, driven by tough discretionary cost discipline, the very early impact of Project Renewal and favorable management incentive costs. We achieved this result despite gross margin being down 10 basis points versus prior year. Importantly, we generated strong cash flow of $561 million in 2011, at the high end of our guidance range of $520 million to $560 million. Our solid cash flow enabled us to pay down $183 million of debt in 2011. And as a result, our strengthened balance sheet has taken another step toward our target leverage ratios. We also used just over $46 million to buy back 3.4 million shares in 2011, a little more than 1% of our float at an average share price of $13.72.