The primary additive in the Lucas Extreme Gun Oil is Zinc Alkyldithiophosphate; looks about 15% per the MSDS. It is a multipurpose additive that is particularly suited for a rust and corrosion inhibitor as well as an effective anti-wear agent. The Zinc Alkyldithiophosphate forms a film and acts as a physical/chemical barrier to water reaching metal surfaces as well a metal to metal contact on sliding surfaces.
I use the Lucas Extreme Gun Oil and Gun grease, it seems to do a great job preventing rust and corrosion and minimizing friction and wear. I'm sure there are other brands that are just as effective. Motor oil will work fine as well, it just has other additives (VI improvers, pour point depressants, anti-foam, detergents, dispersants, etc.) that aren't really necessary for our firearms.
Bottom line: keep your firearms clean and use a lubricant that you have confidence in.