Well, according to the dictionary it means the same thing. Both words are in use but I want to know what is more common.
The US version won't necessarily be the correct spelling! Kate is correct that 'advisor' and 'adviser' can be used interchangeably. Came from the Oxford Online Dictionary so must be true.
Lets assume you are an adviser (or advisor) giving advice. Which is the correct speeling in this case.
As I said qwest, the OED gives both as meaning the same thing - they are both equally acceptable in an English language sense. My personal preference would be the advisor version.
Have to concur with the others, both ways are correct and both are used in the US. There are certain regions of the US that may use one over another but both ways are grammatically correct. I prefer adviser myself.