Optimism about the US economy has increased the price of oil produced by the Organisation of the Petroleum Exporting Countries (OPEC), pushing it up by nearly $2 to $56.05 a barrel, the group announced on Friday.

One barrel (158 litres) of OPEC crude oil rose by $1.96 Thursday, the Vienna-based group announced on Friday, after having reached a six-month high already at mid-week.