Coca-Cola has said it is disappointed with last year's performance.
The soft drink market is becoming increasingly crowded
The comments by Coca-Cola chief executive Neville Isdell came despite the company announcing fourth-quarter results that beat market expectations.
During the three months to 31 December it made profits of $1.2bn (£640m), up from $927m a year earlier.
The world's largest drinks manufacturer said it plans to increase its spend on marketing in the year ahead, especially for Diet Coke.
It has recently started to advertise Diet Coke to men as well as women.
Previously, its advertising for the low-calorie product was only targeted at women.
The company is also introducing a new version of Diet Coke - sweetened with popular sugar substitute Splenda - in the US.
This will be sold alongside the current Diet Coke which is made with aspartame.
Coca-Cola's revenue for the fourth quarter totalled $5.26bn, a 2% increase from the $5.18bn a year earlier.
"We are not satisfied with our performance in 2004," Mr Isdell said.
"Hopefully, what you will sense as we move toward 2005 is the steps that we are taking are the right ones."
For 2004 as a whole, Coca-Cola made profits of $4.8bn, compared with $4.35bn in 2003.
Its shares were up 2.3% in early Wednesday trading in New York.