Apple increased Mac unit sales and market share in the U.S. during the September quarter, according to research firm Gartner. Reversing three consecutive quarters of year-over-year unit sales declines, the market as a whole increased 3.9%, an unexpected gain for the segment, but Apple was able to increase its own unit sales by 6.8%, increasing market share from 8.6% to 8.8%.

While the domestic computer market increased in unit sales, PC-vendors' rush to the bottom in terms of price is taking its toll on revenues, according to Gartner.

"The consumer mobile PC market drove U.S. shipment growth in the third quarter of 2009, fueled by back to school sales," Mikako Kitagawa, principal analyst at Gartner, said in a statement. "However, the results came with a revenue loss because of very steep declines in average selling prices (ASPs). Consumers were comfortable buying PCs, but they were relentlessly looking for bargains. Our preliminary research shows consumer mobile PC ASPs declined more than 20 percent compared to a year ago."

Apple, on the other hand, has taken less of a hit to its ASPs, as the company has decreased prices much less than its competitors, even while its unit sales increase. In Q3 of 2008, Apple sold 1.47 million Macs, and in Q3 of 2009, the firm sold 1.57 million units.

Dell is still #1 in the U.S. market with 4.67 million PCs sold, which alone of the top vendors represents a decline in unit sales of 8.9%. HP is nipping on Dell's heels with 4.57 million units, an increase of 2.7%. Acer took the #3 position with 2.48 million units, a staggering 61.4% year-over-year increase. Acer has lead the field in developing and pushing the netbook market.

Gartner's September Quarter chart

Worldwide, Apple didn't crack the top five, where HP is the number one vendor (16.1 million units), Acer is #2 (12.5 million), and Dell slipped to #3 (10.3 million). Lenova is now #4 (6.9 million units, and Toshiba is #5 (4 million units). Apple is expected to report total sales in the range of 2.5 million, plus or minus a hundred thousand or so.

The worldwide market increased 0.5% year over year, a significant increase considering that Gartner expected to see a fourth quarter of declines, at 5.6%. Gartner also said that worldwide sales increased sequentially from the June quarter 18%, which the firm said was greater than the normal seasonal increase from the June to the September quarter.