MEMPHIS, Tenn., Sept. 19, 2012 (GLOBE NEWSWIRE) -- AutoZone, Inc. (NYSE:AZO) today reported net sales of $2.8 billion for its fourth quarter (16 weeks) ended August 25, 2012, an increase of 4.6% from the fourth quarter of fiscal 2011 (16 weeks). Domestic same store sales, or sales for stores open at least one year, increased 2.1% for the quarter. Net income for the quarter increased $22.3 million, or 7.4%, over the same period last year to $323.7 million, while diluted earnings per share increased 17.8% to $8.46 per share from $7.18 per share in the year-ago quarter. For the quarter, gross profit, as a percentage of sales, was 51.8% (versus 51.2% for last year's quarter). The improvement in gross margin was attributable to an improvement in merchandise margins (55 bps) primarily from lower acquisition costs. Operating expenses, as a percentage of sales, were 31.6% (versus 31.4% last year). The increase in operating expenses, as a percentage of sales, was negatively impacted by higher store payroll (45 bps) and higher self-insurance costs (39 bps), partially offset by lower incentive compensation. For the fiscal year ended August 25, 2012, sales were $8.6 billion, an increase of 6.6% from the prior year, while domestic same store sales were up 3.9%. Operating profit increased 9.0% on an operating margin of 18.9%. For fiscal 2012, net income increased 9.6% to $930 million, while diluted earnings per share for the period increased 20.6% to $23.48 from $19.47. Driven by improved earnings and a declining equity base, return on invested capital reached 33.0%, while full year cash flow before share repurchases and changes in debt was $950 million. Under its share repurchase program, AutoZone repurchased 1.3 million shares of its common stock for $480 million during the fourth quarter, at an average price of $374 per share. For the fiscal year, the Company repurchased 3.8 million shares of its common stock for $1.4 billion, at an average price of $359 per share. At the fiscal year end, the Company had $356 million remaining under its current share repurchase authorization.