The company appeared before Crawley magistrates on 15 December to admit a charge of polluting controlled waters, contrary to section 85(1) of the Water Resources Act 1991.
The court heard that a member of the public reported the pollution to the Environment Agency in June 2002. An investigation traced the pollution to a storm outfall at Thames' Crawley sewage treatment works.
It transpired that the oil was leaking from an oil storage and handling area where mobile pumps were being used next to a 12,000 gallon tank. The Agency found that the company's management of the site was poor and oil storage and handling procedures were unsatisfactory.
The magistrate commented: "It was incomprehensible that Thames Water did not have lockable taps on the oil tank and no protocol for the handling of oil on site."
The case appears to be the company's second conviction in 2003. Its previous court appearance in March ended in fines totalling £27,500 after the company was given three fines for one pollution incident (ENDS Report 339, p 56 ).