The 50e will run on regular unleaded 95 RON (octane)
The 60i being a V8, Although it would run on standard unleaded, I’d run on super unleaded 97-99 RON (depending where you got it) for engine knock reasons and slightly better fuel economy. Octane boosters also exist to add to fuel, though some are better than others,
Depending on the countries you are reading your reviews, petrol could have a different octane rating to that of ours!
In the US & Canada for example, fuel at the pump is based on anti knock index (AKI) and is based on the fuels resistance to engine knocking and is basically based on averaging the fuel Ron (octane) and motor octane number, something we don’t use in the UK, even for sports cars. However, it is useful to look at this index as a comparason and the BMW X5 60i has an Octane rating AKI of 91 or 93 RON. which are standard unleaded exceeds at 95 RON. In comparison US standard unleaded is from memory around 87 RON.