We've heard this before, but ABBA was recently offered $1 billion to reunite on tour -- and they still said no!

Monday half of the Swedish pop quartet were in London for their British book launch party.  Bjorn Ulavaeus and Anni-Frid Lyngstad (once spouses) said that all four members remain good friends, but have no desire to tour again, despite a 10-figure offer.

Frida told London's Evening Standard, "We only have one answer and that is no -- we're not going to do it...no amount of money would change our minds."  But then she back-tracked just a bit.  She added, "Maybe we sometimes say it would be good to do a song together again, just a recording and nothing else, but I don't know if that will happen -- so don't say that we will!"