http://merkel.zoneo.net/Latex/natbib.php

Selecting citation style and punctuation

Use the command \bibpunct with one optional and 6 mandatory arguments:

1. the opening bracket symbol, default = (
2. the closing bracket symbol, default = )
3. the punctuation between multiple citations, default = ;
4. the letter `n' for numerical style, or `s' for numerical superscript style, any other letter for author-year, default = author-year;
5. the punctuation that comes between the author names and the year
6. the punctuation that comes between years or numbers when common author lists are suppressed (default = ,);

The optional argument is the character preceding a post-note, default is a comma plus space. In redefining this character, one must include a space if one is wanted.

Example 1, \bibpunct{[}{]}{,}{a}{}{;} changes the output of

\citepjon90,jon91,jam92

into [Jones et al. 1990; 1991, James et al. 1992].

Example 2, \bibpunct[; ]{(}{)}{,}{a}{}{;} changes the output of

\citep[and references therein]{jon90}

into (Jones et al. 1990; and references therein).