One research firm also estimated Wednesday that Chinese PC maker Lenovo Group Ltd. outsold Hewlett-Packard Co. for the first time to become the world's largest seller of PCs.
Gartner said global PC shipments fell 8.3 percent to 87.5 million, while IDC said the decline was 8.6 percent to 87.8 million. Their reports came hours after a third research firm, IHS iSuppli, projected that PC shipments are bound for their first annual decline in 11 years.
PC makers began the year with hope that a new wave of lightweight laptops called ultrabooks would provide a sales lift. But ultrabooks haven't been compelling enough to overcome the growing popularity of smartphones and tablet computers. Those mobile devices are reducing the need for consumers and businesses to buy new PCs or replace older ones.
Gartner and IDC agreed that Lenovo was the only one of the top four PC makers that saw an increase in shipments, thanks to low prices. Lenovo vaulted onto the international scene when it bought IBM Corp.'s PC division in 2005. It's been the No. 2 PC maker in the world for a few years, behind Hewlett-Packard Co.
According to Gartner, Lenovo saw worldwide shipments grow 9.8 percent to 13.8 million in the third quarter, giving it a market share of 15.7 percent. HP's shipments fell 16 percent from last year to 13.6 million, for a share of 15.5 percent.
IDC had HP on top with 13.9 million and a share of 15.9 percent, with Lenovo close behind at 13.8 million, or 15.7 percent.
HP, which has its headquarters in Palo Alto, Calif., issued a statement saying that some reports "don't measure the market in its entirety. The IDC analysis includes the very important workstation segment and therefore is more comprehensive. In that IDC report, HP occupies the No. 1 position in PCs."
Both reports are based on estimates. Companies will start releasing their numbers over the next few weeks as part of quarterly earnings reports.
Dell Inc. of Round Rock, Texas, and Acer Group of Taiwan are No. 3 and 4 in both reports. AsusTek Computer Inc., also of Taiwan, is fifth.
In the U.S., both had HP as the top PC maker, followed by Dell, Apple Inc., Lenovo and Acer.
As the year winds down, the PC industry is now counting on an upcoming makeover of the Windows operating system to revive interest in desktop and laptop machines.
Windows 8 has been redesigned by Microsoft Corp. so it can power hybrid PCs that can be controlled by touching a display screen or relying on a keyboard and computer mouse. The revamped operating system also works on tablet computers, including one that is being made by Microsoft. If tablets running on Windows catch on, they threaten to siphon even more sales from PCs.
Machines running on Windows 8 are scheduled to go on sale Oct. 26 from Lenovo, HP, Dell, Samsung Electronics Co. and others.
Even with Windows 8, IHS predicts a 1 percent decrease in PC shipments this year to nearly 349 million. Although small, the anticipated decline would be the first time annual PC sales haven't grown since 2001.