According to the latest report from ZenithOptimedia, advertising spending in North America should surpass $154.2 billion this year, growing steadily over the coming years to over $176 billion by 2006. ZenithOptimedia finds that the country?s largest ad spenders have driven growth this year with a 16% increase in spending among these leaders. Zenith notes that its estimate for overall ad spending in the US in 2003 is over $148.8 billion, representing roughly 96% of total ad spending in North America.