The decline in oil prices has been a relief for consumers and a rare piece of positive news in a bleak economic landscape. But for oil producers that have grown accustomed to rising revenue, falling prices are turning into a cause for concern, if not quite panic.

Oil prices have dropped by a third in seven weeks and appear to be headed below the symbolic $100-a-barrel threshold for the first time since March. Though oil remains expensive by historical standards, the speed of the decline is prompting some soul-searching within the OPEC cartel.

Venezuela and Iran, the leading price hawks in the group, said they did not want oil to fall below $100, a price Iran’s oil minister recently said was a “minimum.” Both countries signaled that members of the Organization of the Petroleum Exporting Countries needed to reduce output to bolster prices.

Other OPEC members, like Algeria and Kuwait, fear that high energy costs might jeopardize their exports as the global economy slows. Saudi Arabia, the world’s biggest oil exporter, has not specified a price it considers fair, though King Abdullah has said that $100 was too high.

For OPEC’s leaders, who will meet in Vienna next week, trying to manage the decline in prices is tricky. Cutting production at today’s elevated levels could spark a backlash and paint the cartel as greedy. Conversely, leaving production unchanged at a time when demand growth is slowing could precipitate a price collapse, as in the late 1990s.

“They are playing a balancing game,” said Michael Wittner, the global head for oil research at Societe Generale, in London. “If prices are too high, they will kill the golden goose and hurt consumption. But at the same time, they see the weakening economy and are thinking the world doesn’t need so much oil right now.”

Oil settled at $107.89 a barrel on Thursday, the lowest level in five months. The drop accelerated even after Hurricane Gustav’s passage over the Gulf of Mexico caused modest disruption to oil and gas production.

Despite a fall from the record high of $147.27 a barrel on July 11, oil prices are up 14 percent this year. They have more than quadrupled in five years.

Drivers are getting some relief as gasoline falls from this summer’s records. If oil drops below $100 a barrel, that would most likely drive gasoline prices below $3.50 a gallon, down from July’s peak of $4.11. Gasoline now sells for an average of $3.68 a gallon. But falling oil prices could jeopardize investments in new sources of energy, including alternatives to petroleum, whose economics would look less favorable.

Producers have gotten used to the high prices, which have fueled an unprecedented economic boom in the Middle East, Russia and South America. From the gleaming towers of Abu Dhabi to the new cities burgeoning in Saudi Arabia, producers are relying on their petroleum windfall to develop industries, attract businesses and expand their economies.

Some analysts believe the group next week may opt for an informal cut in production, reducing output without much fanfare, instead of a formal announcement that could prove politically tricky.

Another option may be to convene another meeting in six to eight weeks and announce a big reduction then. The group is already scheduled to meet in December in Algeria, but that could be too late to act if prices keep declining.