[5] Spurred by four Billboard Hot 100 top-40 singles ("Black and Blue", #34; "Finish What Ya Started", #13; "When It's Love", #5; and "Feels So Good", #35), the album eventually sold over 4 million copies.

[8] When Hagar was brought to the studio, Eddie showed a piano and drums demo he recorded with Alex Van Halen, which the band soon developed into the song "When It's Love".

Given the musical parts were finished quicker than the lyrics, Hagar took some weeks off and travelled to his Mexican house at Cabo San Lucas to work on more songs.

"[8] Although it was considered a joke song, "Source of Infection" was written about Eddie's hospitalization with dengue fever during his vacation in Australia in April 1988, celebrating his seventh wedding anniversary with Valerie Bertinelli.

The cover features a black and white photo of the band member's faces partly hidden in shadows, and is also similar to that of Blue Cheer's Vincebus Eruptum (1968) and King Crimson's Red (1974).

Jan had previously appeared playing clarinet on one track, "Big Bad Bill (Is Sweet William Now)", on Van Halen's 1982 album, Diver Down.

He noted that "trading Dave for Sammy sure wrecked their shot at Led Zep of the '80s--master guitarist, signature vocalist, underrated rhythm section."

He said of "Source of Infection": "While Eddie Van Halen sprays you with a machine-gun succession of speed-metal-guitar arpeggios, Sammy Hagar sends out the party invitations with his usual savoir-faire — "Hey!

Still, he stated that "the riffs are complicated, not catchy, the rhythms plod, they don't rock, and Sammy strains to inject some good times by singing too hard."

"[11] Canadian journalist Martin Popoff defined OU812 music as "cynical corporate rock" and found the album "over-produced and actually more commonplace" than its predecessor 5150, implying that "the philosophical soul and warmth" of Van Halen "evaporated when David Lee Roth packed it in.

"[12] In a music magazine interview published a few years after the release of the album, Eddie Van Halen expressed his opinion that the record was not mixed as well as he would have liked: "Sonically it was shit.

There has been speculation that the thin presence of bass guitar in the mix may be related to the Van Halen brothers' rumored growing animosity towards bassist Michael Anthony.