The connection between evolution of regulatory elements and downstream gene expression is incompletely understood in mammals. We carried out a large-scale comparison of matched ChIP-seq and RNA-seq experiments across twenty species of mammals, using liver as a model somatic tissue. Herein we report the RNA-seq dataset, comprising twenty five species of mammals. When analysed alongside our previously reported ChIP-seq experiments, these data reveal a number of insights into how mammalian regulatory evolution propagates into differences in gene expression levels. Please note that all mouse RNA-seq libraries and three out of four human libraries have been previously reported in Array Express submission E-MTAB-4052 and are thus omitted here.