Slumping demand for diet sodas sold by PepsiCo and Coca Cola propelled a decline for the broader industry, as overall sales of carbonated soft drinks dropped for the 11th consecutive year in the U.S. Total volume declined 1.2% in 2015, an acceleration from 2014’s 0.9% drop, as the biggest three players in the category all reported falling demand, according to a new report from industry tracker Beverage Digest.