Oil group OPEC is set on Friday to stick by its policy of unconstrained oil output for another six months, setting aside warnings of a second lurch lower in prices as some members such as Iran look to ramp up exports. With no apparent dissent, the Organization of the Petroleum Exporting Countries will roll over its current output ceiling, renewing support for the shock market treatment it doled out late last year when Saudi Arabia, the world’s top supplier, said it would no longer cut output to keep prices high.