Google Inc. shares have gone past $700 in pre-market trading in the States, adding $100 in less than a month.

New advertising programs and talk of the imminent arrival of the gPhone, as reported in the Wall Street Journal, are thought to be the cause for the increase.

Google shares are now more than twice as expensive as those of Microsoft, Intel and Hewlett-Packard.

"One of the reasons that Google has been such a success story is not only because it's taken market share from its competitors, but also to some extent it's created new opportunities and new markets", Scott Kessler, an analyst at Standard & Poor's in New York, told Bloomberg.