AbstractThe phase behaviour of five distillation fractions of a Fischer‐Tropsch wax were investigated at pressures up to 40 kbar by means of differential thermal analysis. The approximate constancy in the number of significant components (i.e. greater than 5% by wt.) in each wax fraction is probably responsible for them appearing to behave as a series. Similarity of the phase diagrams of the individual wax fractions gave rise to the construction of a ‘master’ phase diagram. A possible new high‐pressure phase was detected in the heaviest fraction, but the possibility of phase separation cannot be e