The 74,000-dwt Emerald Summit (built 2013) is said to have gone to a Greek buyer for $37.5m.
The STX built ship has been for sale for some time and is the only long range 1 (LR1) tanker in Quantum's fleet.
UK based online platform VesselsValue.com says the tanker is worth $43.4m.
VesselsValue says Quantum has a fleet of more than 60 vessels in the water collectively worth in excess of $2bn.
