At which studio was most of Metallica's The Black Album recorded?

Most of Metallica's The Black Album was recorded at One on One Recording Studios in Los Angeles.

The main recording period began there in October 1990 and continued through June 1991. The facility provided the setting for the band's demanding sessions with producer Bob Rock, during which the musicians repeatedly refined performances and arrangements.

The album's production was not limited to one location. Metallica also spent about a week at Little Mountain Sound Studios in Vancouver, British Columbia, and completed additional overdubs and mixing at A&M Studios in Hollywood.

One on One is therefore the principal studio associated with the album, while the other locations were part of the broader production process. The sessions were unusually laborious for Metallica, with many takes reviewed and edited before the final tracks were assembled.