not sure why regex is doing this

Hi, I have a text file that I have to parse and insert into a db. these are a couple of sample lines (they are part of the variable $query) (4536,'golf tournament management',430,0,0), (1434,'Premium golf balls',,,0), I have to replace the blank entries (,,) with NULLs, and I am using this regex: $query = preg_replace('/,\s*,/',',NULL,', $query, -1); after this line, only ONE of the ,, sets is replaced by ,NULL, like this: (4536,'golf tournament management',430,0,0), (1434,'Premium golf balls',NULL,,0), So, my problem is that I have to run the regex twice to replace both sets of ,, with ,NULL, and I really don't want to do that. Why isn't it getting them both with the first regex, and how should I modify it to catch them both? TIA, Craig