I need to do the parameterization of hidden parameters which is passed thro the sessionid. I am having three places in the session id creation in the recorded script. How can I find out which should be used for parameterization? Please suggest.

I am putting my points in precise manner:
1. It is a php based ecommerce web site.
2. When login with userid,password one array is generated and created as a session.
3. When doing add to cart another session is created.
4. During Order placing another session created. These two sessions are not shown in my script separately.
5. In the recorded script it is showing the session id as for example: PHPSESSID=a44... etc some random number.