the mercury racing division says plus, standard mercs (pro) says opti oil
2-Stage Direct Fuel Injection Ignition PCM Digital Inductive Alternator System 60-amp (756 watt) Belt Driven Gear Ratio 1.62:1 Fuel/Oil Ratio Electronic Multipoint Recommended Oil Mercury Premium Plus (TC-W3)
http://www.mercuryracing.com/outboar...rtxs/specs.php