I sense some changes coming in sanctioned oil (Iran as you mentioned, Venezuela possibly).
Reading the news I sense that too but the evidence suggests otherwise.
I can't speak of Venezuela but Iran's sanctions were too long that Iran already found customers to sell oil to (including Europeans!). So in a way there is no need to sell any additional oil to Europe anymore, specially now that Iran is increasing pressure on the West for 43 years of sanctions.
In fact if any sanctions were to be lifted, there is a good chance that mostly Russia oil reaches European markets through Iran.
Hint: A little more than 2 months ago Greece seized an Iranian oil tanker and Iran responded by seizing 2 US oil tankers. The Iranian tanker was actually carrying Russian oil and was heading towards Western Europe.
Already Russians are transporting part of their oil in the stealth mode. Ship-to-ship transfers are taking place and Asian as well as European refineries are being used to produce finished products sourced primarily from the Urals crude.