Most commercial stations are now owned-and-operated or controlled through outsourcing agreements by group owners (either independent companies or network-owned subsidiary groups), with a relatively limited number of companies that remain which own stations in five or fewer markets; a series of station purchases that have occurred since 2011 (when the Sinclair Broadcast Group acquired the Four Points Media Group) has concentrated the number of station owners even further, as a result of increasing competition between over-the-air broadcasters and subscription television outlets as well as to increase leverage in negotiations with cable and satellite providers for retransmission consent (which since the early 2000s, has increasingly become a primary form of revenue for broadcast networks, which have required their affiliates to share a portion of the revenue received by pay television providers as an additional source of operational revenue).