Gravitational collapse scenario: evolution of the C/O ratio as a function of the total mass of solid accreted after the initial formation of the protoplanet. The purple curve corresponds to a formation within the H₂O iceline, and the brown curve to a formation between the H₂O and CO₂ icelines. The orange area gives the 68% confidence interval for the value of the C/O ratio. Dashed vertical lines corresponds to different solid accretion limits discussed in the text.