Guardian News and Media is increasing the price of The Observer by 20p on 14 September making it the most expensive UK Sunday newspaper at £2.90.
The paper has more than doubled in price over the last 10 years, from £1.40, and seen circulation decline by more than 50 per cent in the same period. Retail prices in general have increased by a third in the same period.
The Sunday Times costs £2.50, the Independent on Sunday costs £2.20 and The Sunday Telegraph £2.
The Guardian is the most expensive mainstream national daily newspaper at £1.60.
In July 2014 sales of The Guardian fell 5.2 per cent to an average of 181,181 and sales of The Observer dropped 8.6 per cent year on year to 201,377.
All editorial content for The Guardian and Observer is made available for free online.
A Guardian News & Media spokesperson said: “The quality of our journalism goes from strength to strength and we continue to invest in our print products. Over the last 18 months we have introduced a number of new supplements including Observer Tech Monthly, which is proving extremely popular.
"There are a number of special supplements in the pipeline, and the price rise will allow us to continue to provide premium and innovative print products for our loyal and engaged readers in an increasingly tough market."