Washington (AP) -- Democratic presidential nominee Barack Obama's campaign is shelling out big bucks for tv time.

On Monday, Obama's camp spent $3.3 million, while republican rival John McCain spent $900,000 and the Republican National Committee spent another $700,000 on his behalf. At that rate, Obama will spend more than $90 million on ads through election day.

All whopping numbers, but the disparity between Obama and the republicans is so wide that it has allowed Obama to spend in more states than McCain, to appear more frequently in key markets and to diversify his message by both attacking McCain and promoting his own personal story.

A study by the Wisconsin Advertising Project at the University of Wisconsin-Madison shows with national and state polls showing Obama building a broader lead over McCain, he's switched to a more positive pitch. Last week, only 34 percent of his ads attacked McCain directly while virtually all of McCain's ads attacked Obama.

(Copyright 2008 by The Associated Press. All rights Reserved.)