Possible Duplicate:
Is it proper usage to replace a comma in a list with a semi-colon in this situation (see details)?
When should one use the comma versus the semicolon, and vice versa?
I have a list if items that contain commas - in this case city/state pairs. A co-worker of mine claims that I should promote the list commas to semicolons in this case but I cannot find any style guide which lists this as rule. Is this just urban legend?
example:
The sales team will visit Portland, Oregon; Portland, Maine; Spring Field, Ohio; and Spring Field, Massachusetts.