Brent crude oil was flirting with $85 per barrel on Tuesday, down slightly from a four-year high in the previous trading session. West Text Intermediate (WTI) was posting similar multi-year highs at $75.40.

Both benchmarks are now far removed from the dog days of 2016, when Brent crude was trading as low as $27 a barrel.

The recovery, which has gathered steam over 2018, begs the question: How high can oil prices go?