- Otherwise, historically, at least in the United States, the main reliable measure of quality has been the American Petroleum Institute (API) "Service" rating (buy API SL for older BMWs or API SM or better for newer BMWs) printed on every can of oil sold in the US. This more readily available API quality designation is chronological, i.e., SA, SB, SC, SD, SE, SF, SG, SH, SI, SJ, SK, SL, & SM. Over time, this API quality designation moved higher and higher in the alphabet as more and more problems are specified and overcome by the petroleum engineers (note SA is unspecified, and note each specification exceeds the prior specification).
- Note that anyone who says "use Castrol" or "get Mobil1", without suggesting the BMW or ACEA or API quality rating, isn't providing enough information to make the right quality decision for you; brand and price and label hype are meaningless for this purpose (for example, even some BMW-branded oils don't meet BMW specifications for M cars).