VIENNA — As officials from some of the world’s biggest oil producers arrive here in Vienna, they have plenty to be cheery about.

Oil prices have risen unexpectedly fast of late, surging 20 percent since the beginning of September, providing much-needed money for the strained budgets of the 14 members of the Organization of the Petroleum Exporting Countries.

That leaves OPEC members with a quandary: Do they again extend production cuts first announced a year ago? What had seemed to analysts to be a foregone conclusion now looks to be more complex.

The group of oil exporters, along with some nonmembers like Russia, agreed to the production cuts to ease a glut in the market and bolster prices. To some extent, that appears to have worked. Brent crude oil, the main international benchmark, is trading at around $64 a barrel, even after falling slightly this week. Some analysts see prices topping $70 next year.