Oil prices have declined by over 35% over 6 weeks up to December 2018, after the US granted waivers to countries that allowed them to import oil from Iran for 180 days.  Being a surprise decision, this has meant that oil markets (thinking of shortages) have had to adjust to keeping around 1.5% of global supply (an excess supply) that it previously thought was not going to be in the market
In addition, Russia’s reluctance to cut production, surging US oil production and the difficult US – Saudi Arabia relationship has also weighed on oil prices
Next major milestone for oil markets is December 6, when OPEC and allies officially meet and markets wait on an OPEC decision to reduce output