The Sixth Report and Order also provided for the "intermixture" of VHF and UHF channels in most markets; UHF transmitters in the 1950s were not yet powerful enough, nor receivers sensitive enough (if they included UHF tuners at all - they were not formally required until the 1960s All-Channel Receiver Act), to make UHF viable against entrenched VHF stations. In markets where there were no VHF stations and UHF was the only TV service available, UHF survived. In other markets, which were too small to financially support a television station, too close to VHF outlets in nearby cities, or where UHF was forced to compete with more than one well-established VHF station, UHF had little chance for success.