u.s . containerboard net sales for 2006 were $ 955 million , compared with $ 895 million in 2005 and $ 950 million for 2004 . average sales price realizations in the first quarter of 2006 began the year below first-quarter 2005 levels , but improved sig- nificantly during the second quarter and were higher than in 2005 for the remainder of the year . sales volumes were higher throughout 2006 . operating profits in 2006 were more than double 2005 levels , and 68% ( 68 % ) higher than in 2004