SQL & PL/SQL :: Joining Multiple Tables

I tried to split the query into 2 parts , the outcome is fine but when ever i merge them ( include other table fields ) . The result is 3X3 rows .. it should be just 3 rows

The First Query ( Is running fine , 3 Rows returned )

SELECT
WORKORDER.WONUM,
WORKORDER.ESTSERVCOST,
WPM.ITEMNUM,
WPM.ITEMQTY,
[code]......

The Second Query ( Is running fine also, 3 Rows returned )

SELECT
WORKORDER.WONUM,
WORKORDER.ESTSERVCOST,
WP.DESCRIPTION,
WP.LINECOST
FROM WORKORDER , WPSERVICE WP
WHERE PARENT IS NULL
AND WORKORDER.WONUM = WP.WONUM
AND WORKORDER.WONUM = :WO

The problem occurs when i try to merge both these queries , as the result shows 9 rows ..

SELECT
WORKORDER.WONUM,
WORKORDER.ESTSERVCOST,
WPM.ITEMNUM,
WPM.ITEMQTY,
[code]......