Is it possible to create a pivot table using source data from more than one worksheet?

Yes you can create pivot using multiple Worksheets. But this function is not as flexible as you create pivot table using single sheet.
Sturcture of all the tables must remain same to take the advantage of this feature.
use keyboard short keys to aproach if you are using 2007 version otherwise the multiple table merging option may not be visile to you.

Press Alt + D followed by P
Select third option "Multiple Consoliation Ranges"
Click Next
Select "Select a Single Page Field for me"
Click Next

Now Select First range and Click on ADD
Add
and Select & Add as many ranges you want to consolidate.
Click Next/Finish

Now a Pivot is created using default fields.
Remeber Only First column values will be treated as row label
and First Column Values will be treated as Columns.

you can drag Column values before and after only column values and can change the way of calculation for the column labels.

As I have already stated you that this is not much flexible function but still very useful. you can experience it yourself while using it.