AMSOIL

AMSOIL INC. was founded in 1972 by Albert J. Amatuzio in Superior, Wisconsin, and is widely credited as the first US company to sell a 100% synthetic motor oil meeting API service requirements. The Signature Series passenger-car line — branded with the ASL (5W-30) / ALM (5W-20) / AMR (5W-50) product codes — is the brand's flagship for extended drain intervals, supported by published TBN, NOACK, and Sequence IVA wear data on the manufacturer product page.

AMSOIL is privately held and remains independent of the major oil refiners — base stocks (PAO Group IV and hydrogenated Group III) are sourced from suppliers and blended at the Superior plant. The brand sells primarily through its dealer network and its own e-commerce site rather than big-box retail, which is part of why the same product line ships in different package sizes than competing synthetics typically found at AutoZone or Walmart.