Oil prices jumped more than 2 per cent to an eight-month high above $73 a barrel today, as a sudden spike in Brent buying pinned on fund positioning ushered out the market’s best quarterly gain since 1990.

While the rally drew support from fresh attacks on oil facilities in Nigeria as well as improving risk sentiment aided by rising equity markets, traders said those factors were secondary to the sudden big Brent bid orders that triggered the frenzy, overwhelming liquidity during the thin Asian day.

Trading volume in both Brent and U.S. crude oil futures surged to more than 10 times the norm for the Asian time zone as prices leapt more than $1.50 in under half an hour around 3am, the sort of move typically only seen in the event of hurricanes or other major disruptions.

“It feels like short-covering because of stop orders left overnight,” said a trader with a global investment bank.

Both prices and volumes cooled slightly by midday, with US crude for August delivery up $1.29 at $72.78 a barrel by 5.05am, off its earlier eight-month high of $73.38. August trade was 12,400 lots versus a few thousand lots normally.

The main focus was on London ICE Brent crude, with volume in the front-month August contract surging to more than 17,000 lots versus the less than 1,000 lots normally, and prices spiking to a peak of $73.50 a barrel.

Traders said bids for 500 or 600 lot clips spooked a market accustomed to 10-20 lot bids. By 5.07am, Brent was up $1.66 to $72.65 a barrel.

Trading activity in US gasoline and heating oil, which expire at the end of the day, was minimal.

Most traders were quick to point the finger at one or several big funds, either closing out loss-making positions, dressing up returns by boosting prices at the end of the quarter or perhaps taking a position in anticipation of a third quarter influx of new funds.

“This could be end of quarter movement, and traders are trying to push prices higher and then selling before closing their books,” said Mark Pervan, senior commodities analyst at ANZ Bank. “I haven’t seen any new catalyst on the news front.”

Others were more blunt about the unexplained surge in volume, which seemed to be counter-productive given the fact that any sizeable bid would drive up prices due to thin Asian liquidity.