A RECORD seizure of expensive cannabis oil has been made by customs officers at the Kwai Chung container port. Three litres of the oil and 60 kilograms of herbal cannabis, worth a total of $4 million, were confiscated. Senior Superintendent Lawrence Wong Sau-pui of the Customs Drug Investigation Bureau said hashish oil was unpopular among local drug abusers. ''Nevertheless, we believe there are still some users who pour the oil on to the cigarette end or on a tobacco paper before lighting it up,'' he said. The hashish oil is priced four times higher than herbal cannabis, which sells for between $30 and $60 per gram. In the operation on Tuesday officers arrested three Nigerian tourists, aged 27 to 37, for alleged involvement in the Lagos-based drug trafficking syndicate. The trio had been under customs surveillance in the past two weeks after a tip-off that they were arranging to take a consignment out of the container port. The cargo, which was at first found to contain 72 cartons of beer, arrived in Hong Kong on December 1, from Nigeria via Europe, the Middle East and Singapore. During the bureau's investigation, officers of the Ship Search and Cargo command were told the cargo contained ivory tusks. The consignment was subsequently detained pending a check by customs officials. ''Knowing that the cargo had been detained, the suspects asked the shipping company concerned to try to re-export the consignment to Germany, which was not possible,'' Superintendent Wong said. Bureau officers arrested the Nigerians at a guesthouse in Chungking Mansions at about 3 pm on Tuesday. Some shipping documents were seized. They were taken to the container port where customs officers found 60 kilograms of herbal cannabis and nine bottles of hashish oil concealed inside 32 pieces of hollowed wooden blocks used to secure the cartons of beer.