As of Wednesday morning, Mitt Romney and Republican groups supporting his candidacy have bought more than $30 million worth of advertising this week in nine swing states, far outpacing President Barack Obama and his allies, according to a source monitoring ad buys.

Obama and his Democratic allies are spending $21.7 million in the same states.

Showing its financial muscle, when you compare just what the campaigns are spending on ads, excluding outside groups, the Obama team this week outpaces Romney's -- $17.8 million to $12.3 million.

Because we are in the home stretch, ad buys are being added constantly so the numbers are in flux.

Several super PACs supporting - Restore Our Future and American Crossroads - have just announced multi-million dollar ad buys so the Republican tally will rise in the coming days.

Both the campaigns and allied groups are concentrating most of their activity in the same swing states: Colorado, Florida, Iowa, Nevada, New Hampshire, North Carolina, Ohio, Virginia and Wisconsin.