Had 2 Games the last days:
1st Game (0.25f) - standard size, no debug options, no special options (no raging barbs etc)
Got the first OOS after ~turn 150 seems coming in the AI turn. We fought some barbs and orthus but no OOS. After the first OOS we got 3-4 more after ~10 turns each. We kicked then Bannor (8 Citys conquered without OOS) and the OOS stoppt. Kicked then around 10 Citys of Sheaim without OOS but got 2 OOS for the last 2 Citys of him. The only Special on this last 2 Citys where, that they had Ashen Veil (The only Citys so far, rest had Octo, Fellow or Runes). Got a OOS for taken each.
I Fought most of the Game with Swordsmen (Elf), later upgraded to Macemen. Besides of the last 2 Citys i got no OOS from combat. Besides of some Pyrozombis only normal enemys.
Unique Wonders on the Map where: Yggdrasil, Letum Frigus, Maelstrom and Pyre of the Seraphic so no raging Barbatmos on the map.
2nd Game (0.25h) - Huge Continents, no debug options, no special options.
We managed without OOS till the first "human" barbs show up (Goblins/Orcs). From then their was a 50% Chance to get a OOS from Combat with Barbs dosnt matter if attack or defend. We got many additional OOS at the end/begin of the turn, so maybe produced by the AI. We got OOS nearly every turn so we stopped after ~30 OOS/Rejoins. Their where some turns of "peace" in the Game, between large waves of Barbs and they where pretty OOS free.
In both Games we picked the AI-Civs cause i´ve read Balseraph and Clan causing some trouble in Multiplayer so we avoid them.
Sorry that i cant give more Infos, we had no Log on and no Debugoptions...
From what if seen in both games, the most OOS came from the combat with barbs, in the 1st game we had standard size with 5 players, so their was not much room for barbs to spawn, but it was their. Barbs managed to get a City from my friend, even it was short.
In the 2nd game was much more unexplored room cause we played on huge with 7 players. So a lot barbs came from many directions.