This is the motor oil I use the most. Some info from their website:

Royal Purple Motor Oil delivers superior protection and improves performance in four-cycle gasoline and diesel engines. It increases horsepower and torque, saves fuels and reduces heat, wear and emissions. It has unsurpassed oxidation stability that allows for extended oil drains and fewer oil changes, which saves you time and money and reduces the impact on the environment.

Royal Purple’s motor oils for passenger cars and trucks are API licensed. For those seeking enhanced performance in high performance vehicles not under warranty, we recommend our XPR – Extreme Performance and Racing motor oil.

Royal Purple’s performance advantages come from a blend of synthetic oils plus Royal Purple’s proprietary Synerlec technology. Royal Purple Motor Oil is compatible with other mineral and synthetic motor oils. It’s available in 0W40, 5W20, 5W30, 5W40, 10W30, 10W40, 15W40, 20W50, SAE 30, SAE 40 and SAE 50 weights.

For improved performance in two-cycle engines, check out Royal Purple 2-Cycle TCW III.

You can follow them on Twitter at @RoyalPurpleInc