Oil fell today as dealers tracked last-ditch efforts between global powers and Iran to reach a deal on Tehran's nuclear programme and ease sanctions imposed on the crude producer.
Brent North Sea crude for delivery in May slid $1.23 to $55.06 a barrel in London deals. US benchmark West Texas Intermediate (WTI) for May shed $1.11 to $47.57 a barrel.
Marathon talks aimed at preventing Iran from acquiring nuclear weapons went into a final nail-biting day today, with Russia saying the chances were "high" of reaching a historic framework deal by midnight.
Russian Foreign Minister Sergei Lavrov was rushing back to the Swiss city of Lausanne to "take part in the final part of the ministerial meeting of the six powers."
An army of technical and sanctions experts had worked into the early hours of this morning, exchanging documents to form the basis of an accord.
The two sides hope to seal a political framework aimed at ending a nuclear standoff that has been threatening to escalate dangerously for 12 years.
US Secretary of State John Kerry, in Lausanne since Wednesday in the latest in a series of meetings around the world with his Iranian counterpart Mohammad Javad Zarif, said last night there "still remain some difficult issues."
Under the deal, due to be finalised by June 30, the powers want Iran to scale back its nuclear programme to give the world ample notice of any dash to make a bomb by extending the so-called "breakout" time.
In return diplomatically isolated Tehran, which denies wanting atomic weapons, is demanding the lifting of sanctions that have strangled its economy.
With the world's fourth biggest oil and second biggest gas reserves, the energy industry is the cornerstone of Iran's economy, but it has been hit hard by the American and European embargo imposed since 2012.
