Oil pared gains in post-settlement trading after API data shows big surprise build in U.S. crude stocks.
Brent crude rose 46 cents, or 0.96 percent at $49.63 a barrel, after hitting an intraday high of $51.20. The global benchmark settled more than 3 percent lower on Monday after rallying 20 percent between the beginning of the month and Aug. 19.
U.S. crude's West Texas Intermediate was last up 0.74 percent at $47.76 a barrel, after settling at $48.10 a barrel, up 69 cents, or 1.46 percent. WTI broke a seven-day winning streak in the previous session.
Oil prices had been positive after Reuters reported Iran is sending positive signals that it may support joint action to prop up the oil market, citing sources in OPEC and the oil industry.
OPEC's third-largest producer has been boosting output after the lifting of Western sanctions in January. Tehran refused to join a previous attempt this year by OPEC plus non-members such as Russia to stabilize production, and talks collapsed in April.
Though Iran has not yet decided whether to join a new effort, Tehran appears to be more willing to reach an understanding with other oil producers, the sources said.
"Iran is reaching its pre-sanctions production level soon and after that it can cooperate with the others," said a source familiar with Iranian thinking after Venezuelan Oil Minister Eulogio Del Pino's visit to Tehran.
Russia, which in April was ready to freeze production, now wants to see an internal agreement among OPEC before it commits to rejoining an initiative.
"Negotiations are ongoing. I see positive signs coming from OPEC 'majors'," said a senior industry source familiar with the discussions, referring to Riyadh and Tehran.
The International Energy Forum, which groups producers and consumers, is due to meet on Sept. 26-28 in Algiers. Iran confirmed its participation in a meeting at the forum, an OPEC source said on Tuesday.
A two-year long selloff in oil has severely hurt the economies of Venezuela, Iraq and Nigeria. Those nations are seen as more anxious to boost crude prices than OPEC producers such as Saudi Arabia and Iran, which are more keen in protecting market share.
According to Rystad Energy, Saudi Arabia and Iran had the lowest oil production costs in OPEC, at around $9 a barrel each, while Iraq's was about $10. Venezuela's cost was more than double of those, at $27 a barrel, while Nigeria's was the highest at $29.
Many analysts remain skeptical of the effort following the Iran report.
"The current price level of well over $40 does not provide non-OPEC producers with any kind of motivation to support oil prices by cutting or maintaining current production levels," said Tamas Varga, analyst at London-based energy broker PVM.
Earlier on Tuesday, Brent fell below $49 a barrel, giving up part of August's strong rally, as signs of rising supply outweighed hopes that producing nations will agree to steps to support prices.
Among the developments that point to higher supply, Iraq resumed pumping crude through a northern pipeline halted earlier this year. Further, Iraqi Oil Minister Jabar Ali al-Luaib, at a meeting in Baghdad on Tuesday, told foreign oil companies to increase oil output and exports.
Iraq's call for more output came on top of worries about burgeoning Chinese fuel exports, more Nigerian crude shipments and a rising U.S. oil rig count.
In a report, Goldman Sachs said talk of an output freeze by the Organization of the Petroleum Exporting Countries and a weak dollar had helped drive prices up this month, but neither was enough to sustain current levels.
"We see too many headwinds and logistical challenges to a meaningful deal," Morgan Stanley said in a report.
In focus later on Tuesday will be the first of this week's reports on U.S. inventories, which analysts expect will show a decline in crude and gasoline stocks. The American Petroleum Institute, an industry group, is scheduled to release its data at 4:30 p.m. ET (2030 GMT), while the government's supply report is due on Wednesday.
Investors are also looking for clues on whether the U.S. Federal Reserve will raise interest rates this year. Fed Chair Janet Yellen will give a speech at a global central banking conference in Jackson Hole, Wyoming, on Friday.