John Fredriksen’s SFL Corp, a New York-listed owner of 71 ships, announced on Wednesday that it has bought four more tankers for $222.5m.

It did not identify the ships, other than to say they are suezmaxes built in 2015 and 2020 and are equipped with modern eco-design features and exhaust gas cleaning systems.

The deal includes six-year time charters with a subsidiary of Koch Industries that add about $250m to SFL’s fixed-rate backlog, it added.