At which London studio was Master of Reality recorded?

Master of Reality was recorded at Island Studios in London.

The album was made during recording sessions held from February to April 1971, with producer Rodger Bain overseeing the work. Island Studios occupied a converted church building at 8–10 Basing Street in Notting Hill and was operated by Island Records. The unusual room and studio design gave the facility a distinctive place in London’s recording history.

Black Sabbath had already completed much of Paranoid at Island, so the studio was closely connected with the band’s early sound. During Master of Reality, Tony Iommi and Geezer Butler used downtuned instruments, helping produce the heavier, lower sound that became one of the album’s signatures. The record was released by Vertigo on 6 August 1971.

The studio name can cause confusion because it was later renamed Basing Street Studios and eventually became associated with Sarm West. The album’s original recording credit, however, is Island Studios, not Trident, Olympic, or Abbey Road.