The Organization of the Petroleum Exporting Countries said in its April monthly report that oil prices rose more than 20 percent in March, continuing a slow recovery from the huge drop of 2014-15.
"Positive market sentiments continue to arise from the output freeze plan being considered by major crude exporters," as well as an expected fall in output in the United States and elsewhere, OPEC said.
All oil producers, not just those in the 13-nation OPEC but also non-cartel members like Russia, have suffered from the more than 60-percent drop in oil prices since mid-2014.
A agreement in Doha on Sunday to freeze production would, in theory at least, help boost prices and help repair their in some cases -- for example Venezuela -- tattered public finances.
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But a deal among the 15 or so oil producers representing around 75 percent of global output expected at the meeting is far from guaranteed.
OPEC member Iran has so far rejected attempts to freeze production as it ramps up output following the lifting of sanctions this year as part of 2015's nuclear deal with major powers.