On the A320 max imbalance between wing tanks before ECAM warning is 1500kg......500kg imbalance for take off.....
On the B737, the Boeing Ops manual states...
max qty wings 4827kg each
max qty centre 7448kg
max lateral between wings 453kg taxi take off flight or landing.
Both main tanks must be full, if centre tank contains more than 453kg, presumably limited by MZFW
Hope that helps
Tailwinds
