This article seeks to assess in detail the extent of levelling of regional varieties in the so-called collateral-language areas (Langue d'Oïl and Franco-Provençal) of France over the course of the 20th century. By comparing the ‘classic’ accounts of regionally marked pronunciation among speakers born in the first half of the century (Martinet, 1945; Walter, 1982; Carton, Rossi, Autesserre and Léon, 1983) with studies based on informants born since 1965, I seek to characterise and remap the varieties that still show divergence from the supra-local or levelled variety, which has been referred to as Oïl French, in the ancestral Langue d'Oïl and Franco-Provençal regions and to define the areas beyond these ancestral collateral-language areas, where speakers of 40 years or under at the time of writing may be fairly characterised as conforming to the supralocal norm.