Extension of non "b"

[Baaksida]

Just got my first Non-immigrant "B" Visa last week, for double entry.

Was puzzled though by the inscription "No extension possible..." on the visa. Didn't want to upset the embassy employee with too many questions...

So my question is now, can I extend the first 90 days of this visa by another 30 days at Immigration (90 d + 30 d + 90 d + 30 d  ??), or do I definitely have to leave the country for a border run after these 90 days, activating my second entry ?      

[lopburi3]

Ninty days is the max.  For tourist it can be 60 + 30 (and if the stars are right a little more - but that would put you in violation of the 90 address reporting rule so maybe not possiable now).  But your visa allows the full 90 days.  Before it ends you need to make a border crossing and get your second 90 days.