This paper presents the physicochemical methodology especially nondestructive testing and microanalysis applied for the documentation of the condition of oil paintings and oil sketches on paper support. The research is focused on the effect of the oil binder on the paper and the changes caused during the progress of deterioration in order to provide criteria for the better evaluation of the condition. Six original artworks representative samples of the Greek artists of the 18th-20th century, belonging to the National Gallery - Museum and Alexandros Soutzos Museum were investigated. The research was supported by experimental laboratory study of artificially aged mock ups made of linseed oil and different paper supports. The research methodology involved non-destructive imaging (UVF, multispectral), FORS, colourimetry, microscopic techniques (optical VLM/FLM, SEM) and micro analytical techniques (HS-SPME-GC-MS, SEM–EDX, and FTIR) for the examination and the identification of the materials and the degradation products of the original artworks and the mock-ups before and after ageing. The present article discusses the evaluation of the obtained results and the assessment of the techniques employed as far as the applicability and the efficacy in the study of the particular subject. The appraisal of the methodology is expected to contribute to the development of an experimental tool for the evaluation of the condition of this particular type of works.