Oxidation stability tests have been developed for estimation of the long term storage stability of diesel fuels. Currently, several oxidation stability test methods (eg. ENISO12205, Rancimat (EN15751), PetroOXY (EN16091)) are used for this purpose. It is common for these tests to have an elevated temperature and to add oxygen or air to accelerate the oxidation of the test fuel, and hence accelerate conduction of the test. It has been under discussion whether these tests actually represent real-life conditions. Also, it has been proposed that these oxidation stability tests could be used to estimate the thermal stability of the diesel fuels. In many cases the correlation to real-life is unclear.Stability of EN590 B0 (winter and summer grade) and B7, B30, EN590 with 30% HVO, 100% HVO, WWFC category 4 diesel, Swedish class 1 as well as the effect of cetane improver was evaluated with different oxidation stability methods. Also real-life thermal stability and fuel quality changes were studied in a common rail engine (Peugeot DW10) with all test fuels except B30.The tested fuels did not show any signs of oxidation or deterioration during the engine test. Contrary to expectations, the fuels showed better results in the oxidation stability tests after being exposed to high temperature and pressure in the engine's injection system. PetroOXY, delta TAN and hydroperoxides results improved during the engine test. No changes in ENISO12205 and 13 weeks storage test results were seen before and after the engine test.