Gel permeation chromatography inductively coupled plasma high-resolution mass spectrometry (GPC ICP HR MS) was used for the understanding of the evolution of two crude oil cut samples after their dilution. We first studied different method parameters to compare two GPC procedures already published [flow rate, column set, and presence or not of the tetrahydrofuran (THF) stabilizer]. Thus, the principal parameters affecting the molecular size distribution and its evolution were demonstrated. The column set and flow rate can drastically affect the molecular size distribution of the sample. Moreover, an evolution of the size distribution of the complexes of vanadium, nickel, and sulfur into higher molecular weight compounds was observed over time. The study led to the recommendation of the sample preparation to the same day of the analysis to obtain reproducible data.