The anti-whaling group Sea Shepherd claims it has evidence a refuelling ship servicing Japan's whaling fleet has spilled oil in Australian waters.

The group says it collected samples from an oil-slick spotted yesterday near the South Korean-flagged Sun Laurel in the Australian Antarctic Territory.

Sea Shepherd has four ships trailing the Japanese fleet's annual whale hunt in the Southern Ocean.

Former Greens Senator and Sea Shepherd board member Bob Brown says the type of fuel detected is prohibited in Antarctic waters.

"Crew of the Sam Simon, the Sea Shepherd ship, have been able to smell oil, they've seen the oil slick, they've sampled oil, but the authorities that should be protecting this pristine Antarctic eco-system and Antarctic Ocean are nowhere to be seen," he said.

The Japanese agency behind the whaling operation has been contacted for comment.