Purchase Order Query Pulling Duplicate Records

Hello Friends,

Just wanted to find out why the below query is picking duplicate rows.Have i missed any joins here?

SELECT   v.segment1             po_number,
msi.segment1                    item,
pvs.vendor_site_code            supplier_site,
pol.line_num                    po_line_num,
pll.shipment_num                shipment_num,
pol.quantity                    po_qty,
pll.quantity_received           quantity_received,
pll.quantity_billed             quantity_billed,
pll.quantity_cancelled          quantity_cancelled,
pll.unit_meas_lookup_code       uom,
cc.segment1                    division,
v.vendor_name                   supplier_name,
hl.location_code                ship_to_location
from
         po_headers_all h,
         po_lines_all pol,
         po_line_locations_all pll,
         po_distributions_all pda,