By enabling users to freely share news content from their newsfeed or from news websites, Twitter contributes to reconfiguring the balance of the content offered. This study on the sharing of French journalistic articles has enabled the authors to characterize in general terms a major trend in this reconfiguration, i.e. the fact that the news offer loses its original pluralism as it becomes concentrated on a very limited number of media. Going through Twitter enables the better-known media with stronger identities to play a key part in the structure of sharing. This effect is however not due exclusively to the media’s productivity (number of articles put online), and to the size of its acquired audience (number of daily visits to its website). To better understand all the factors driving it, the authors analyse the relational rationales of sharing on socio-digital networks.