Bond coat (BC) oxidation as well as bond coat depletion of Al are still believed to be the major degradation mechanisms with respect to the lifetime of thermal barrier coating (TBC) systems. For more than one decade the influence of oxidation behaviour on the service life of components was described by simply the thermally grown oxide (TGO) thickness. However, it has recently been shown that the adherence of the top coat is also an important parameter for the durability of the system. Fracture mechanics in conjunction with finite element modelling (FEM) has also provided valuable insight with regards to the mechanical breakdown and failure of the thermal barrier coating systems. In this study the top coat lifetime is described as being limited by both "mechanical" failure of the top coat and bond coat depletion of Al. The empirical results are introduced by considering three spallation cases, namely, thermal fatigue failure, thermal ageing failure and Al depletion failure. Top coat and TGO degradation due to thermal fatigue is characterized by in-situ acoustic emission analysis, where the data were acquired during cyclic oxidation testing. Degradation due to thermal aging and TGO growth is characterized by four-point bend testing of isothermally preoxidized samples. This four-point bend test also uses acoustic emission analysis for the purpose of determining the critical strains of the top coat and TGO, where the critical strains for the onset of delamination and the onset of through cracking are found. Bond coat depletion of Al is modelled by considering the diffusion of Al into both the TGO and substrate. The diffusion model results are compared to the measured TGO growth kinetics and the Al concentration profile measured with an electron beam micro probe. Top coat spallation occurs when the Al content within the bond coat reaches a critical value. The three mechanisms and the measured results are embedded into a lifetime prediction model. This model is applied to both isothermal and cyclic oxidation samples. The results are compared to measured life times up to 5000 hr in the temperature range of 950degreesC through 1150degreesC.