Most light aircraft run MIL-H-5606, mineral oil. only 2000 psi.
The commercial a/c type that i work on uses this oil in the hyd systems at a normal working pressure of approx 3,000 psi. (Aeroshell Fluid 41 ). I have also worked on a Mil A/C that uses this oil at 287 bar ( approx 4,000 psi ), It was called OM15 on the Mil A/C.
HTH.