As OPEC starts to make its production cuts work, the true impact of its actions is perhaps most in evidence in an obscure part of the physical oil market. While Brent futures, a benchmark based on North Sea supply, are trading about $4 a barrel higher than their peak in June, the price of cheaper Middle East crude is rising faster still. The gap between the two varieties — now the smallest in 15 months — reveals where buyers are experiencing the greatest supply restrictions. It also has the potential to influence where oil flows. Saudi Arabia and its neighboring countries mostly pump lower quality oil, known in the industry as heavy crude. So when production from Organization of Petroleum Exporting Countries drops, the price difference — or spread — between those grades and higher quality light crude such as Brent […]