Brent oil may rise to $150 a barrel this year if diplomatic relations between Iran and the west worsen, Barclays PLC forecasts.

Brent may surpass its record high of $147 a barrel if political tensions surrounding Iran’s nuclear program heighten, even if there is no military conflict or closure of the Strait of Hormuz, the bank said in a report today. This would cause the average price of the North Sea crude in 2012 to exceed Barclays’ base-case forecast of $115 by about $20, the bank said. Brent traded at about $122 in London today.

“Quarterly averages of $140 per barrel or $150 per barrel are distinctly possible” in the third and fourth quarters of 2012, London-based analyst Amrita Sen wrote. “This is not our current base case, though it does seem to be moving closer to becoming reality.”

Oil demand growth in Asia is rising faster than current prices indicate, while global supplies have been reduced by 1.2 million barrels a day amid disruptions in Sudan, Syria and Yemen, according to Barclays. That’s left worldwide spare production capacity at the “extremely thin” level of 1.7 million barrels, the bank estimates.