Industry analysts last week said Mac sales in the U.S. increased by as much as 15% in the second quarter, making Apple one of only two of the top five computer makers to post positive gains.
Apple will release its global sales numbers later today during an earnings call with Wall Street after the financial markets close at 4 p.m. ET.
U.S. Mac sales rose by 14.7% in the second quarter compared to the same period in 2010, according to IDC, while rival research firm Gartner estimated that Apple's numbers climbed 8.5% for the three months that ended June 30.
Of the top five U.S. computer sellers -- Acer, Apple, Dell, Hewlett-Packard and Toshiba -- only Apple and Toshiba showed year-over-year sales gains. Industry-wide, U.S. sales were down in the second quarter; IDC had the decline at 4.2%, while Gartner estimated the drop at 5.6%.
Acer, whose sales have heavily relied on netbooks, fell the sharpest, dropping by 25.4% in IDC's tally and sliding 22.6% in Gartner's. Netbook sales have been hammered by competition from tablets like Apple's iPad, and lackluster consumer sales in general.
Apple's U.S. Mac second-quarter sales also increased dramatically over the previous quarter, both IDC and Gartner said: IDC had the quarter-over-quarter increase at 39.4%, while Gartner forecast a 21.7% gain.
Second-quarter Mac sales in the U.S. are typically strong because public school purchases begin in that period.
Apple boosted its share of the U.S. market to nearly 11% during the second quarter, both IDC and Gartner said. That put Apple in the No. 3 spot behind HP and Dell, and gave it the edge over former third-place Toshiba.
Gartner credited the iMac refresh of early May for the jump in sales.
"The preliminary findings show Apple's performance far exceed the industry average, partly driven by an iMac refreshment that attracted both consumers and buyers in the education sector," the firm said in a statement.
Apple typically sees a short-lived bump in sales when it launches new Macs, Stephen Baker of the NPD Group said when the iMac line was revamped with faster Intel quad-core processors.
The company should get another boost when it refreshes the MacBook Air , its popular lightweight notebook. New MacBook Airs could debut as soon as this week, according to several reports by Apple-centric blogs Monday.
Today, Brian White, an analyst with Ticonderoga Securities, said Apple will claim worldwide Mac sales of nearly 4 million machines, an 8.4% gain over the previous quarter and a 14.7% increase from the same quarter in 2010.
If White's projections are accurate, Apple will have outpaced the computer industry average for the 21st consecutive quarter.
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer or subscribe to Gregg's RSS feed . His e-mail address is firstname.lastname@example.org .
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This story, "Apple's U.S. Mac Sales Gains Again Hit Double Digits, Experts Forecast" was originally published by Computerworld.