He said most of the oil emulsified into the choppy water and westerly winds, gusting to 40 knots, helped confine the remaining oil within the boom at the corner of No 2 wharf where it was recovered.
Maritime New Zealand was notified and a wildlife team put in place. The team was stood down at 7.30pm.
In November, council, port staff and the Coastguard had held an oil spill training exercise at the same location.
The Maritime Transport Act requires the council to complete two oil-spill exercises a year.
A 300m boom is now stored on the wharf, meaning its deployment takes just 30 minutes with two people, compared with the previous 90 minutes and up to eight people.
Any oil washed up on nearby beaches will be recovered by the HBRC.