The conformation of a polypeptide chain adsorbed at an oil (hydrophobic solution)/water (aqueous solution) interface has often been described as a succession of loops in either one phase or the other. If this view is accepted, each loop should be formed of a sequence of amino acids having a sufficient affinity for its solvent. Some amino-acid sequences, having no affinity for either solvent, may lie in the interfacial plane. For entropic reasons, the general conformation of such an isolated molecule in the interfacial layer should be a cylinder with its axis perpendicular to the interface. The cylinder should in fact be divided into two pancakes, each pancake corresponding to the part of the cylinder floating in a solvent and gathering the loops that are in rather good solvent conditions in this phase. In the semi-dilute regime, the pancakes should overlap and the interfacial pressure should be the sum of the pressures of the layers formed in each solvent. A simplified molecular model has been used to calculate the thermodynamic properties of the interfacial layer. This model is a dibloc polymer and the chain in each pancake is squeezed between the interfacial plane at a distance close to the size of the loops. Calculations were performed using scaling law arguments. The simplified model predicts the value of the exponent of the power law relating the interfacial pressure to the interfacial concentration. The value of the exponent should reflect the quality of the solvent of one phase or of the two phases. This exponent has been calculated for data previously obtained with haemoglobin adsorbed at different oil/water or air/water interfaces. The experimental values are of the expected order of magnitudes and can be used to hypothesize the conformation of haemoglobin at fluid interfaces.