ISO Specs 2005 - currently the universal specification available. 2010 has been introduced but availability is still sporadic with even the main ports (with the odd exception) not able to guarantee its availability 100% of the time. In its absence usually 2005 is the specification offered and guaranteed - although there are still places that offer it with exceptions on certain parameters.
1996 has mostly been phased out - indeed it is rare to come across a port or supplier that can only meet 1996.
To see the relevant fuel spec, click on the relevant grade on the left toolbar.