Hewlett-Packard maintained its lead over Dell as the world's largest PC supplier in the third quarter of 2007, extending a slim margin it established last year, market researcher IDC said Wednesday.

HP's PC market share increased in the U.S., fast approaching leader Dell, whose market share fell, according to IDC's quarterly report of PC unit shipments.

The number of PCs shipped worldwide was 66.85 million, a 15.5 percent year-over-year increase. The jump was attributed to a strong demand for portable computers, including laptops and ultraportables, and PC demand in the SMB market. While adoption of laptops and ultraportables increased worldwide, desktop shipments decreased in the U.S., the survey said.

HP shipped 13.1 million PCs worldwide in the third quarter, a 19.6 percent market share and a 33 percent year-over-year increase. Dell followed in second place, shipping 10.18 million units, a 3.8 percent increase over the previous year, IDC said. Lenovo, Acer, and Toshiba. followed in the third, fourth and fifth spots, respectively.

Acer, which became the world's third-largest PC vendor when it acquired Gateway on Wednesday, recorded a 59.2 percent increase in worldwide PC shipments. These quarterly figures are before the acquisition was final.

In the U.S., Dell shipped 5.01 million PCs in the third quarter, a 4.8 percent drop compared to last year. HP's PC shipments increased 16.9 percent to 4.35 million, accounting for 24.3 percent of the market. In third place was Apple, whose year-over-year shipments increased 15.9 percent to 1.13 million. Gateway, which shipped 865,000 PCs, recorded a 14.2 percent year-over-year fall.

HP has momentum on its side, while Dell is in the process of restructuring, said Loren Loverde, program director at IDC. At the same time, many users are making the conversion from desktops to laptops as they get more experience using PCs, Loverde said.

The survey defined PCs as desktops, notebooks, ultraportables, and Intel-based servers. The statistics do not include handhelds or smartphones, according to IDC.

Demand for PCs over the next few years will continue to increase due to vendor competition and increased commercial spending, IDC projected.