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That’s a really good question! I’d say that TOST is just a single data point in hydraulic oil selection. There’s pretty ample evidence to suggest that hydraulic oils (depending on the application of course) rarely fail through oxidation. It’s typically a contamination issue. I’ve attached a tech topic from ExxonMobil that covers the subject in a decent amount of detail. Do you have a specific hydraulic application that you are selecting for?