OPEC oil ministers reached a final agreement Tuesday to extend their existing oil output pact for six months, Venezuelan oil minister Arturo Herandez Grisanti said.

The agreement was reached at the 13-nation cartel's regular midyear meeting.Organization of Petroleum Exporting Countries ministers had haggled over whether to extend the production accord by three months or by six months, delegation sources said.

On Monday, the ministers held informal talks in small groups, which is how the ministers seem to prefer to negotiate.

The ministers, who began their conference on Saturday, gathered to decide whether to change the agreement among 12 of the producers to limit output to 15.06 million barrels a day.

The accord, which would have expired June 30, was designed to maintain oil prices at $18 a barrel, but it failed to achieve that goal.

High-level sources in several delegations, speaking on condition of anonymity earlier, said a majority of the OPEC ministers had favored the shorter extension.

One senior Arab source, who spoke on condition of anomymity, said it would make more sense to renew the accord for the third quarter and then meet again in the autumn.

But the minority, favoring the longer extension, reportedly includes the influential Saudis, OPEC's biggest producers.

Oil markets were disappointed by the developments in Vienna, even though traders had been expecting an extension of the accord. Analysts said the prospect of yet another extension highlighted OPEC's inability to overcome its differences on production levels.