Get a tool like TOAD which can be used to really fine tune a query.
The stuff that Tim sais is also very important, limit your records as soon as possible so there are less records to scan for each part of the join. I shrank a query from 12 commas in the iteration count to less than 100 million iteration simply by filter the where clause earlier

>Can you post the explain plan for each query:
>
>Example:
>
>EXPLAIN PLAN FOR
>SELECT Tab1.*, Tab2.*, Tab3.*, Tab4.*, Tab5.* FROM tab1, tab2, tab3, tab4, tab5 WHERE (tab1.column1=tab5.column1) AND (tab1.column2=tab2.column2) AND (tab2.column3=tab4.column3) AND (tab2.column4=tab3.column4)
> AND tab1.column5=to_date('1900-01-01','YYYY-MM-DD')
> AND tab2.column6='03' AND tab2.column7='AC';
>
>EXPLAIN PLAN FOR
>SELECT Tab1.*, Tab2.*, Tab3.*, Tab4.*, Tab5.* FROM tab1, tab2, tab3, tab4, tab5 WHERE (tab1.column1=tab5.column1) AND (tab1.column2=tab2.column2) AND (tab2.column3=tab4.column3) AND (tab2.column4=tab3.column4)
> AND tab1.column5=to_date('1900-01-01','YYYY-MM-DD');
>
>EXPLAIN PLAN FOR
>SELECT Tab1.*, Tab2.*, Tab3.*, Tab4.*, Tab5.* FROM tab1, tab2, tab3, tab4, tab5 WHERE (tab1.column1=tab5.column1) AND (tab1.column2=tab2.column2) AND (tab2.column3=tab4.column3) AND (tab2.column4=tab3.column4)
>AND tab2.column6='03' AND tab2.column7='AC';
>
>
>How much data is in each table....
>
>A quick quess without the extra explain plan info would be :
>Try putting the 'AC' part first...
>SELECT Tab1.*, Tab2.*, Tab3.*, Tab4.*, Tab5.* FROM tab1, tab2, tab3, tab4, tab5 WHERE tab2.column7='AC' AND
>(tab1.column1=tab5.column1) AND (tab1.column2=tab2.column2) AND (tab2.column3=tab4.column3) AND (tab2.column4=tab3.column4)
> AND tab1.column5=to_date('1900-01-01','YYYY-MM-DD')
> AND tab2.column6='03';
>
>in general Order the where clause as follows...
>
>where table with most data first join AND table with less data at end join...
>I.E. move the where clauses around so that the largest tables come first...
>
>
>I'm thinking Hash Join too but need to see the execution plan.
>
>Note if you run the queries in that order you would expect the last 2 to be faster becuase the rows would now be in the DB Buffer (memory). To get real results you will need to run each query with a clean buffer...
>
>HTH