Opec on Tuesday agreed a surprise cut in supplies from April 1, propelling world oil prices higher and drawing a caution from the United States not to hurt economic growth.
The decision cuts output limits for the group that controls half the world's oil trade to 23.5 million barrels a day from April 1.
The deal is designed to help prop up oil prices when demand slackens after the northern hemisphere winter, without sending prices spiralling too high by cutting immediately.
The delegate said the agreement was to implement the reduction from the start of April, even though Opec is already scheduled to meet again on March 31.
An Opec official said the group had also agreed to immediately eliminate 1.5 million barrels a day of quota-busting now being pumped above existing supply quotas.
The Organisation of the Petroleum Exporting Countries has been flouting self-imposed production limits to contain a winter price spike.
Oil prices rose sharply on the deal. US crude at 1420 GMT was up 52 cents at $33.35, valuing Opec reference basket above the group's preferred $22-$28 target range.
"The decision to rein in overproduction is firm now," Saudi Oil Minister Ali al-Naimi told Reuters shortly before Tuesday's meeting started. Naimi said projections for a heavy seasonal second quarter fall in demand should not be taken lightly.
"If this is taken as a serious consideration then the leakage must stop," the Saudi minister said.
Saudi Arabia's insistence that it wants $25 for Opec crude will be put to the test soon as it decides export flows for March.
Riyadh has softened its tone on oil price policy since Opec last met in December.
Naimi said at the time that higher prices were justified by the impact of the weak dollar on producers' spending power.
Since then, and again in Algiers, he has made a point of re-emphasising Riyadh's commitment to Opec's central $25 target.