Google to buy mobile ad network for $750 million

MOUNTAIN VIEW, Calif. — Google Inc. is stepping up its push to sell advertising on cell phones and other mobile gadgets. It has agreed to buy a mobile ad network, AdMob, for $750 million in stock.

Google already has a mobile ad delivery system, DoubleClick Mobile. The company says that buying AdMob will give it more expertise in a market that is expected to grow rapidly over the next several years.