We know a lot of PS3 owners are slowly starting to get tired of watching their HDD space fill up with game installs and Bethesda knows this as well. In a recent interview with Joystiq, Pete Hines, Bethesda's marketing genius has confirmed that Fallout 3 will not require an upfront install like so many games before it. When questioned specifically about the mandatory install, he had this to say:
"The answer to that is no, there isn't," states Hines concerning Fallout 3 on the PS3. "That doesn't mean we don't use the hard drive, just that it does it in the background as opposed to a large, upfront install."
Hines wouldn't clarify how much space the game would take up behind the scenes as you played but he did say it would be approximately the same amount as Oblivion. Elder Scrolls IV took up about 4-5 GBs worth of space but you always had the option to delete the data after every playthrough and just let it build back up; something other titles aren't really giving you the option to do.