U.S. Internet giant Google Inc., which has been relatively slow in expanding market presence in South Korea, was fast catching up to local rivals in advertisement sales last year, industry sources said Thursday. According to the sources who have access to internal data, Google raked in some 100 billion won (US$93.8 million) in revenue from its online display adverts in South Korea last year, a significant improvement from the 40 billion won posted a year earlier.