Noam Chomsky and Ed Herman have done excellent comparative research demonstrating exactly that in great detail. For example by comparing coverage of events by the U.S. and its allies to similar events by enemies, finding consistent and strong bias in the mainstream media.

They also develop a theory, more of an explanation, that this is essentially because mainstream media is funded through advertising which then naturally biases it towards the interests of the business elite. That is how we get thought control in a democratic society.

See Manufacturing Consent and Necessary Illusions for numerous cases. Wonderful books. See also Alex Carey's work on corporate propaganda, Taking the Risk Out of Democracy.