If you plan to bowl in tournys, then I think you'd need at least 6, if you bowl in different houses, then at least 3 that match the oil for the houses, if you stay in one house, or they are set the same , oil conditions, then you can get away with 2, but 3 would probably be better, all plus a spare ball.
I personally own 6, carry 3 and a spare. I bowl mainly in one house, that's all that is within an hours drive of me, so I know the conditions. No matter what you see, read here, it all has to do with what can YOU do with the ball/s you have. If you can move in, out, then one ball can do the work of maybe two, so it all depends on your ability and conditions you have.
Now that I have confused you, hope than helps.
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AZ Guy aka: R & L Bowlers Pro
rlbowlerspro@cox.net
www.rlbowlerspro.comSleep is over rated.