CBS announced its fourth quarter earnings on Wednesday and the company saw a 21% increase in local broadcasting revenue for the period.

The revenue increase was due primarily to growth in advertising sales.  Advertising revenue increased 28% in the final quarter of 2010 as stations benefited from an increase in political advertising surrounding last year’s midterm elections.

“CBS’s momentum accelerated throughout 2010, culminating in our best results of the year in the fourth quarter,” said Leslie Moonves, CBS’s president and CEO. “Every one of our operating groups achieved solid quarterly revenue growth.”

For the entire year of 2010, CBS’s local broadcasting revenues were up 18% compared to the previous year.