Store procedure performance

Hi,

I've  concurrent program  based on a stored procedure which is is running very slow. There is only one query in the stored procedure and when the query is executed independetly it completes in a couple of mins.

But for the same parameters the concurrent program run for few hours. The query in the procedure uses table : ap_invoices_all, ap_inv_dist_all,po_vends,po_vend_sites_all, gl_code_comb, ap_terms, ap_inv_payments, ap_checks_all.

Can anyone please suggest the reason why concurrent program is running slow.

Thanks,

Sushma.