VIENNA — OPEC ended a meeting on Thursday without striking a deal to reduce oil output and without any clear sign one would be reached when officials from the organization, Russia and other oil producers reconvene Friday.

As he climbed into a car on a rainy street outside OPEC headquarters, Saudi Arabia’s energy minister, Khalid al-Falih, told reporters he was “not confident” an agreement that would keep supply and demand in balance was within reach.

Mr. Falih had said in the morning that “all options” were on the table, but that a reduction of one million barrels a day — roughly 1 percent of the global oil supply — would be “adequate” to balance the markets. One million barrels a day would likely be considered a modest cut by traders. He said he had heard a range of numbers discussed, from 500,000 to 1.5 million barrels a day.

Ann-Louise Hittle, an analyst at the market research firm Wood Mackenzie, said that it was not surprising for the group to fall short of a deal on its first day of meeting.