MotorStorm: Pacific Rift seems to be one from the information at the related link
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No you can't play multiplayer offline only single player. But you can play it online with other online players.
Yes of course you can. Everyone who buys a PS3 and does not get a online connection installs the game they purchased at the stores and then plays them offline.
Portal 2 is a co-op game rated E10+
Not on the same xbox/ps3 no unfortunately.
It depends on the game, but 7 controllers can work on the PS3 and some games have more than 4 players although many only have a single offline player. Online MAG may have 250 players i think 2 players