SAN FRANCISCO - Newspaper advertising has sunk to a 25-year low as marketers shift more of their spending to the Internet.

The nearly $26 billion spent on newspaper ads last year is the lowest amount since 1985 when the total stood at $25 billion. Adjusted for inflation, the 1985 volume would translate to about $49 billion today.

The 2010 figures were released Tuesday by the Newspaper Association of America, the industry's biggest trade group. Print advertising has been on the decline for four years, dramatically shrinking newspaper publishers' main source of income.

While the economy has slowly improved since 2009, newspaper ad sales continue to wane due customers' shift toward online advertising. Newspaper advertising totaled $7.3 billion in the last three months of 2010, down 4.7 percent from the prior year.