Oil prices have risen as high as $75 a barrel for the first time in four years. But what has driven the rally and will it continue? Here are the five key areas to watch: 1. Supply and demand The simplest reason for the rise in oil prices is that markets have tightened markedly over the past 18 months. Inventories of crude that had built up during the glut of 2014-16 have largely been worked off because of strong demand driven by a booming global economy and supply cuts by Opec and Russia. The International Energy Agency said last week that Opec could soon declare “mission accomplished” if it were targeting reducing global oil inventories back in line with the five-year average. Some believe that underestimates how tight the market is as demand has soared by more than 5m b/d, or more than 5 per cent, in the past three years, with global crude consumption expected to top 100m b/d for the first time later this year. That means higher inventories should be required to provide the same number of days’ cover for oil refineries. “The overhang has largely been cleared,” said Olivier Jakob at Petromatrix. “The market is not extremely tight yet but with the glut taken away the conditions are there for the price to improve.”