Adverse pressure gradient (APG) turbulent boundary layer (TBL) flow is an important flow among the family of wall-bounded turbulent flows because it is encountered in numerous engineering applications, including diffusers, turbine blades, aircraft wings, wind turbine blades, as well as marine vessel flow. It has the potential to cause flow separation, resulting in significant losses such as loss of lift and an increase in pressure drag, which are typically accompanied by highly undesirable unsteady surface pressure forces. In order to minimise and/or control the flow separation due to APG environments, it is essential to understand the physics of the APG-TBL flow to allow appropriate designs of efficient aerodynamic surfaces and/or the development and application of control methodologies to delay or prevent separation. This paper reports on the design of an experiment to establish an experimental self-similar APG-TBL at the verge of separation in order to characterise its statistical structure and the contribution of the Reynolds stresses to the wall shear stress via quadrant analysis decomposition in conjunction with the Renard & Deck (RD) decomposition [1] of the mean skin friction. In this study, high-spatial-resolution (HSR) two-component – two-dimensional (2C-2D) particle image velocimetry (PIV) is employed to measure the self-similar APG-TBL flow. The measurements of the self-similar APG-TBL at the verge of separation, referred to as ‘strong APG-TBL’, are compared with similar HSR 2C-2D PIV measurements of a TBL under zero and a mild APG to characterise the effect of the APG on the TBL. In the strong APG-TBL, the outer scaled profiles of the first- and second-order statistics, and the defect velocity exhibit self-similarity over the measured streamwise domain of 3.3δ . The quadrant decomposition of the velocity fluctuations shows that the formation of the outer peak in the Reynolds shear stress profile under APG is due to the energisation of sweep motions of high-momentum fluid in the outer region of the boundary layer. The RD decomposition of the mean skin friction shows that the skin friction has more significant contributions from ejections than sweeps. It is also observed that the contribution of the turbulent kinetic energy to skin friction generation is enhanced with increasing APG. This enhancement is due to the emergence of the outer peaks with a corresponding diminishing of the inner peaks in the turbulence production profiles. The skewness and flatness profiles show that the zero skewness and minimum flatness locations of the streamwise and wall-normal velocity fluctuations collapse with the location of the maximum Reynolds streamwise stress in the TBLs, irrespective of the pressure gradient imposed on the TBL.