Apple's shares have received a boost as momentum builds for the San Francisco Macworld Expo.

Top US analyst Gerard Klauer Mattison has raised Apple's ranking from "neutral" to "outperform", predicting an increase in share price until the Expo opens on January 7.

The analyst says in Yahoo Finance that benefits will follow from the upgrade cycle of Mac OS X increasing with the release of new products.

Amid growing hype Apple has revealed it will launch new products at the show.

Apple CEO Steve Jobs will lift the lid on product releases during his keynote address on January 7, which will be webcast live over the Internet.