DME Oman's premium rose more than $1 from the previous session to $4.22 a barrel on Tuesday, Reuters calculations showed.

Supply concerns ahead of US sanctions against Iran and strong crude demand from China and Japan before winter have pushed up spot crude premiums this month.

But the more than $1 jump in Oman's premium puzzled industry players, given that it is occurring in a week when most of the oil industry is tied up with meetings at APPEC in Singapore.

Brent shot to its highest in four years on Tuesday, catapulted by imminent US sanctions on Iranian crude exports and the apparent reluctance of OPEC and Russia to raise output to offset the potential hit to global supply.