Castrol BioBar is a range of environmentally acceptable hydraulic fluids which can replace conventional mineral oils in hydraulic equipment where leakage or spillage may result in escape into the marine environment. Castrol BioBar hydraulic fluids are formulated from synthetic ester base oils which are selected to give a wide operating temperature range and long service life. Extensive testing of Castrol BioBar and hydraulic system components (in particular, elastomer seals) has confirmed good compatibility with standard components, which can allow conversion of existing equipment without the need for major changes.