Aiming to predict the strength of bonded joints by techniques such as cohesive zone models (CZM), it is highly relevant to estimate the adhesive strength and fracture toughness (G(C)). Here, the tensile and shear fracture toughness (G(IC) and G(IIC), respectively) and the corresponding mixed-mode behaviour acquire special relevancy. However, it is known that these parameters are highly dependent on the adhesive thickness (t(A)). The present work experimentally addresses the t(A) effect on the mixed-mode behaviour of bonded joints, namely on the tensile and shear fracture energies (G(I) and G(II), respectively), using the Single-Leg Bending (SLB) test. Different data reduction schemes were applied. With this purpose, the respective resistance curves (R-curves) were calculated, which enabled plotting the respective fracture envelope for a sample t(A) by the knowledge of the pure-mode G(IC) and G(IIC). Overall, it was possible to obtain a good agreement between methods for the mixed-mode G(I) and G(II) calculation and to estimate the most suitable fracture envelope of the adhesive for a given t(A). The compliance-based beam method (CBBM) was found to be particularly suited to perform data reduction, since it accounts for the adhesives' ductility and it is not affected by crack length (a) measuring errors.